Remove GetAt from string classes

This method duplicates the behaviour of the const [] operator and
doesn't offer any additional safety. Folding them into one
implementation.

SetAt is retained, since implementing the non-const [] operator to
replace SetAt has potential performance concerns. Specifically many
non-obvious cases of reading an element using [] will cause a realloc
& copy.

BUG=pdfium:860

Change-Id: I3ef5e5e5a15376f040256b646eb0d90636e24b67
Reviewed-on: https://pdfium-review.googlesource.com/10870
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>

20 files changed, 141 insertions, 195 deletions

diff --git a/core/fpdfapi/font/cpdf_cidfont.cpp b/core/fpdfapi/font/cpdf_cidfont.cpp
index 8cb59de739..9a2261caa9 100644
--- a/core/fpdfapi/font/cpdf_cidfont.cpp
+++ b/core/fpdfapi/font/cpdf_cidfont.cpp
@@ -627,7 +627,7 @@ int CPDF_CIDFont::GlyphFromCharCode(uint32_t charcode, bool* pVertGlyph) {
       if (uni_str.IsEmpty())
         return cid;
 
-      unicode = uni_str.GetAt(0);
+      unicode = uni_str[0];
 #endif
     } else {
       if (cid && m_pCID2UnicodeMap && m_pCID2UnicodeMap->IsLoaded())
@@ -637,7 +637,7 @@ int CPDF_CIDFont::GlyphFromCharCode(uint32_t charcode, bool* pVertGlyph) {
       if (unicode == 0) {
         CFX_WideString unicode_str = UnicodeFromCharCode(charcode);
         if (!unicode_str.IsEmpty())
-          unicode = unicode_str.GetAt(0);
+          unicode = unicode_str[0];
       }
     }
     FXFT_Face face = m_Font.GetFace();
@@ -735,7 +735,7 @@ int CPDF_CIDFont::GlyphFromCharCode(uint32_t charcode, bool* pVertGlyph) {
       if (unicode_str.IsEmpty())
         return -1;
 
-      charcode = unicode_str.GetAt(0);
+      charcode = unicode_str[0];
     }
     return GetGlyphIndex(charcode, pVertGlyph);
   }
diff --git a/core/fpdfapi/font/cpdf_cmapparser.cpp b/core/fpdfapi/font/cpdf_cmapparser.cpp
index cbf693966e..272f8deb34 100644
--- a/core/fpdfapi/font/cpdf_cmapparser.cpp
+++ b/core/fpdfapi/font/cpdf_cmapparser.cpp
@@ -121,7 +121,7 @@ void CPDF_CMapParser::ParseWord(const CFX_ByteStringC& word) {
       }
       m_Status = 0;
     } else {
-      if (word.GetLength() == 0 || word.GetAt(0) != '<') {
+      if (word.GetLength() == 0 || word[0] != '<') {
         return;
       }
       if (m_CodeSeq % 2) {
@@ -140,18 +140,17 @@ uint32_t CPDF_CMapParser::CMap_GetCode(const CFX_ByteStringC& word) {
   if (word.IsEmpty())
     return 0;
   pdfium::base::CheckedNumeric<uint32_t> num = 0;
-  if (word.GetAt(0) == '<') {
-    for (int i = 1; i < word.GetLength() && std::isxdigit(word.GetAt(i)); ++i) {
-      num = num * 16 + FXSYS_HexCharToInt(word.GetAt(i));
+  if (word[0] == '<') {
+    for (int i = 1; i < word.GetLength() && std::isxdigit(word[i]); ++i) {
+      num = num * 16 + FXSYS_HexCharToInt(word[i]);
       if (!num.IsValid())
         return 0;
     }
     return num.ValueOrDie();
   }
 
-  for (int i = 0; i < word.GetLength() && std::isdigit(word.GetAt(i)); ++i) {
-    num =
-        num * 10 + FXSYS_DecimalCharToInt(static_cast<wchar_t>(word.GetAt(i)));
+  for (int i = 0; i < word.GetLength() && std::isdigit(word[i]); ++i) {
+    num = num * 10 + FXSYS_DecimalCharToInt(static_cast<wchar_t>(word[i]));
     if (!num.IsValid())
       return 0;
   }
@@ -162,12 +161,12 @@ uint32_t CPDF_CMapParser::CMap_GetCode(const CFX_ByteStringC& word) {
 bool CPDF_CMapParser::CMap_GetCodeRange(CPDF_CMap::CodeRange& range,
                                         const CFX_ByteStringC& first,
                                         const CFX_ByteStringC& second) {
-  if (first.GetLength() == 0 || first.GetAt(0) != '<')
+  if (first.GetLength() == 0 || first[0] != '<')
     return false;
 
   int i;
   for (i = 1; i < first.GetLength(); ++i) {
-    if (first.GetAt(i) == '>') {
+    if (first[i] == '>') {
       break;
     }
   }
@@ -176,8 +175,8 @@ bool CPDF_CMapParser::CMap_GetCodeRange(CPDF_CMap::CodeRange& range,
     return false;
 
   for (i = 0; i < range.m_CharSize; ++i) {
-    uint8_t digit1 = first.GetAt(i * 2 + 1);
-    uint8_t digit2 = first.GetAt(i * 2 + 2);
+    uint8_t digit1 = first[i * 2 + 1];
+    uint8_t digit2 = first[i * 2 + 2];
     range.m_Lower[i] =
         FXSYS_HexCharToInt(digit1) * 16 + FXSYS_HexCharToInt(digit2);
   }
@@ -185,10 +184,10 @@ bool CPDF_CMapParser::CMap_GetCodeRange(CPDF_CMap::CodeRange& range,
   uint32_t size = second.GetLength();
   for (i = 0; i < range.m_CharSize; ++i) {
     uint8_t digit1 = ((uint32_t)i * 2 + 1 < size)
-                         ? second.GetAt((FX_STRSIZE)i * 2 + 1)
+                         ? second[static_cast<FX_STRSIZE>(i * 2 + 1)]
                          : '0';
     uint8_t digit2 = ((uint32_t)i * 2 + 2 < size)
-                         ? second.GetAt((FX_STRSIZE)i * 2 + 2)
+                         ? second[static_cast<FX_STRSIZE>(i * 2 + 2)]
                          : '0';
     range.m_Upper[i] =
         FXSYS_HexCharToInt(digit1) * 16 + FXSYS_HexCharToInt(digit2);
diff --git a/core/fpdfapi/font/cpdf_font.cpp b/core/fpdfapi/font/cpdf_font.cpp
index 82f9be3361..0fd8b45326 100644
--- a/core/fpdfapi/font/cpdf_font.cpp
+++ b/core/fpdfapi/font/cpdf_font.cpp
@@ -467,7 +467,7 @@ int CPDF_Font::FallbackGlyphFromCharcode(int fallbackFont, uint32_t charcode) {
     return -1;
 
   CFX_WideString str = UnicodeFromCharCode(charcode);
-  uint32_t unicode = !str.IsEmpty() ? str.GetAt(0) : charcode;
+  uint32_t unicode = !str.IsEmpty() ? str[0] : charcode;
   int glyph =
       FXFT_Get_Char_Index(m_FontFallbacks[fallbackFont]->GetFace(), unicode);
   if (glyph == 0)
diff --git a/core/fpdfapi/font/cpdf_tounicodemap.cpp b/core/fpdfapi/font/cpdf_tounicodemap.cpp
index 30bf0317ee..9076f4a737 100644
--- a/core/fpdfapi/font/cpdf_tounicodemap.cpp
+++ b/core/fpdfapi/font/cpdf_tounicodemap.cpp
@@ -147,7 +147,7 @@ void CPDF_ToUnicodeMap::Load(CPDF_Stream* pStream) {
           continue;
         }
         if (len == 1) {
-          m_Map[srccode] = destcode.GetAt(0);
+          m_Map[srccode] = destcode[0];
         } else {
           m_Map[srccode] = GetUnicode();
           m_MultiCharBuf.AppendChar(destcode.GetLength());
@@ -178,7 +178,7 @@ void CPDF_ToUnicodeMap::Load(CPDF_Stream* pStream) {
               continue;
             }
             if (len == 1) {
-              m_Map[code] = destcode.GetAt(0);
+              m_Map[code] = destcode[0];
             } else {
               m_Map[code] = GetUnicode();
               m_MultiCharBuf.AppendChar(destcode.GetLength());
diff --git a/core/fpdfapi/render/cpdf_charposlist.cpp b/core/fpdfapi/render/cpdf_charposlist.cpp
index a87fc3334e..f5882d9944 100644
--- a/core/fpdfapi/render/cpdf_charposlist.cpp
+++ b/core/fpdfapi/render/cpdf_charposlist.cpp
@@ -38,7 +38,7 @@ void CPDF_CharPosList::Load(const std::vector<uint32_t>& charCodes,
     if (pCIDFont)
       charpos.m_bFontStyle = true;
     CFX_WideString unicode = pFont->UnicodeFromCharCode(CharCode);
-    charpos.m_Unicode = !unicode.IsEmpty() ? unicode.GetAt(0) : CharCode;
+    charpos.m_Unicode = !unicode.IsEmpty() ? unicode[0] : CharCode;
     charpos.m_GlyphIndex = pFont->GlyphFromCharCode(CharCode, &bVert);
     uint32_t GlyphID = charpos.m_GlyphIndex;
 #if _FXM_PLATFORM_ == _FXM_PLATFORM_APPLE_
diff --git a/core/fpdfdoc/cpdf_filespec.cpp b/core/fpdfdoc/cpdf_filespec.cpp
index 5ef6f466c5..e34f54e4e1 100644
--- a/core/fpdfdoc/cpdf_filespec.cpp
+++ b/core/fpdfdoc/cpdf_filespec.cpp
@@ -69,13 +69,13 @@ CFX_WideString CPDF_FileSpec::DecodeFileName(const CFX_WideString& filepath) {
   return ChangeSlashToPlatform(filepath.c_str());
 #elif _FXM_PLATFORM_ == _FXM_PLATFORM_WINDOWS_
 
-  if (filepath.GetAt(0) != L'/')
+  if (filepath[0] != L'/')
     return ChangeSlashToPlatform(filepath.c_str());
-  if (filepath.GetAt(1) == L'/')
+  if (filepath[1] == L'/')
     return ChangeSlashToPlatform(filepath.c_str() + 1);
-  if (filepath.GetAt(2) == L'/') {
+  if (filepath[2] == L'/') {
     CFX_WideString result;
-    result += filepath.GetAt(1);
+    result += filepath[1];
     result += L':';
     result += ChangeSlashToPlatform(filepath.c_str() + 2);
     return result;
@@ -158,19 +158,19 @@ CFX_WideString CPDF_FileSpec::EncodeFileName(const CFX_WideString& filepath) {
     return CFX_WideString();
 
 #if _FXM_PLATFORM_ == _FXM_PLATFORM_WINDOWS_
-  if (filepath.GetAt(1) == L':') {
+  if (filepath[1] == L':') {
     CFX_WideString result(L'/');
-    result += filepath.GetAt(0);
-    if (filepath.GetAt(2) != L'\\')
+    result += filepath[0];
+    if (filepath[2] != L'\\')
       result += L'/';
 
     result += ChangeSlashToPDF(filepath.c_str() + 2);
     return result;
   }
-  if (filepath.GetAt(0) == L'\\' && filepath.GetAt(1) == L'\\')
+  if (filepath[0] == L'\\' && filepath[1] == L'\\')
     return ChangeSlashToPDF(filepath.c_str() + 1);
 
-  if (filepath.GetAt(0) == L'\\')
+  if (filepath[0] == L'\\')
     return L'/' + ChangeSlashToPDF(filepath.c_str());
   return ChangeSlashToPDF(filepath.c_str());
 #elif _FXM_PLATFORM_ == _FXM_PLATFORM_APPLE_
diff --git a/core/fpdfdoc/cpdf_variabletext.cpp b/core/fpdfdoc/cpdf_variabletext.cpp
index 74a5e3adfc..877f8ca01e 100644
--- a/core/fpdfdoc/cpdf_variabletext.cpp
+++ b/core/fpdfdoc/cpdf_variabletext.cpp
@@ -358,11 +358,11 @@ CPVT_WordPlace CPDF_VariableText::InsertText(const CPVT_WordPlace& place,
   CPVT_WordPlace wp = place;
   for (int32_t i = 0, sz = swText.GetLength(); i < sz; i++) {
     CPVT_WordPlace oldwp = wp;
-    uint16_t word = swText.GetAt(i);
+    uint16_t word = swText[i];
     switch (word) {
       case 0x0D:
         if (m_bMultiLine) {
-          if (swText.GetAt(i + 1) == 0x0A)
+          if (swText[i + 1] == 0x0A)
             i += 1;
 
           wp = InsertSection(wp, nullptr, nullptr);
@@ -370,7 +370,7 @@ CPVT_WordPlace CPDF_VariableText::InsertText(const CPVT_WordPlace& place,
         break;
       case 0x0A:
         if (m_bMultiLine) {
-          if (swText.GetAt(i + 1) == 0x0D)
+          if (swText[i + 1] == 0x0D)
             i += 1;
 
           wp = InsertSection(wp, nullptr, nullptr);
@@ -426,11 +426,11 @@ void CPDF_VariableText::SetText(const CFX_WideString& swText) {
     if (m_nCharArray > 0 && nCharCount >= m_nCharArray)
       break;
 
-    uint16_t word = swText.GetAt(i);
+    uint16_t word = swText[i];
     switch (word) {
       case 0x0D:
         if (m_bMultiLine) {
-          if (i + 1 < sz && swText.GetAt(i + 1) == 0x0A)
+          if (i + 1 < sz && swText[i + 1] == 0x0A)
             i++;
           wp.AdvanceSection();
           AddSection(wp, secinfo);
@@ -438,7 +438,7 @@ void CPDF_VariableText::SetText(const CFX_WideString& swText) {
         break;
       case 0x0A:
         if (m_bMultiLine) {
-          if (i + 1 < sz && swText.GetAt(i + 1) == 0x0D)
+          if (i + 1 < sz && swText[i + 1] == 0x0D)
             i++;
           wp.AdvanceSection();
           AddSection(wp, secinfo);
diff --git a/core/fpdfdoc/cpvt_generateap.cpp b/core/fpdfdoc/cpvt_generateap.cpp
index d1abde681d..9b5a82a055 100644
--- a/core/fpdfdoc/cpvt_generateap.cpp
+++ b/core/fpdfdoc/cpvt_generateap.cpp
@@ -123,7 +123,7 @@ bool GenerateWidgetAP(CPDF_Document* pDoc,
       dsBorder = CPVT_Dash(pArray->GetIntegerAt(0), pArray->GetIntegerAt(1),
                            pArray->GetIntegerAt(2));
     }
-    switch (pBSDict->GetStringFor("S").GetAt(0)) {
+    switch (pBSDict->GetStringFor("S")[0]) {
       case 'S':
         nBorderStyle = BorderStyle::SOLID;
         break;
diff --git a/core/fpdftext/cpdf_linkextract.cpp b/core/fpdftext/cpdf_linkextract.cpp
index d795e71639..fb228ec832 100644
--- a/core/fpdftext/cpdf_linkextract.cpp
+++ b/core/fpdftext/cpdf_linkextract.cpp
@@ -152,7 +152,7 @@ void CPDF_LinkExtract::ParseLink() {
 
       if (strBeCheck.GetLength() > 5) {
         while (strBeCheck.GetLength() > 0) {
-          wchar_t ch = strBeCheck.GetAt(strBeCheck.GetLength() - 1);
+          wchar_t ch = strBeCheck[strBeCheck.GetLength() - 1];
           if (ch == L')' || ch == L',' || ch == L'>' || ch == L'.') {
             strBeCheck = strBeCheck.Left(strBeCheck.GetLength() - 1);
             nCount--;
@@ -242,7 +242,7 @@ bool CPDF_LinkExtract::CheckMailLink(CFX_WideString* str) {
   // Check the local part.
   int pPos = aPos;  // Used to track the position of '@' or '.'.
   for (int i = aPos - 1; i >= 0; i--) {
-    wchar_t ch = str->GetAt(i);
+    wchar_t ch = (*str)[i];
     if (ch == L'_' || ch == L'-' || FXSYS_iswalnum(ch))
       continue;
 
@@ -278,7 +278,7 @@ bool CPDF_LinkExtract::CheckMailLink(CFX_WideString* str) {
   int nLen = str->GetLength();
   pPos = 0;  // Used to track the position of '.'.
   for (int i = aPos + 1; i < nLen; i++) {
-    wchar_t wch = str->GetAt(i);
+    wchar_t wch = (*str)[i];
     if (wch == L'-' || FXSYS_iswalnum(wch))
       continue;
 
diff --git a/core/fpdftext/cpdf_textpage.cpp b/core/fpdftext/cpdf_textpage.cpp
index 1470ad700d..a4c8b8fba0 100644
--- a/core/fpdftext/cpdf_textpage.cpp
+++ b/core/fpdftext/cpdf_textpage.cpp
@@ -701,7 +701,7 @@ void CPDF_TextPage::CloseTempLine() {
   CFX_WideString str = m_TempTextBuf.MakeString();
   bool bPrevSpace = false;
   for (int i = 0; i < str.GetLength(); i++) {
-    if (str.GetAt(i) != ' ') {
+    if (str[i] != ' ') {
       bPrevSpace = false;
       continue;
     }
@@ -841,8 +841,7 @@ FPDFText_MarkedContent CPDF_TextPage::PreMarkedContent(PDFTEXT_Obj Obj) {
   CPDF_Font* pFont = pTextObj->GetFont();
   bExist = false;
   for (FX_STRSIZE i = 0; i < nItems; i++) {
-    if (pFont->CharCodeFromUnicode(actText.GetAt(i)) !=
-        CPDF_Font::kInvalidCharCode) {
+    if (pFont->CharCodeFromUnicode(actText[i]) != CPDF_Font::kInvalidCharCode) {
       bExist = true;
       break;
     }
@@ -852,7 +851,7 @@ FPDFText_MarkedContent CPDF_TextPage::PreMarkedContent(PDFTEXT_Obj Obj) {
 
   bExist = false;
   for (FX_STRSIZE i = 0; i < nItems; i++) {
-    wchar_t wChar = actText.GetAt(i);
+    wchar_t wChar = actText[i];
     if ((wChar > 0x80 && wChar < 0xFFFD) || (wChar <= 0x80 && isprint(wChar))) {
       bExist = true;
       break;
@@ -889,7 +888,7 @@ void CPDF_TextPage::ProcessMarkedContent(PDFTEXT_Obj Obj) {
   matrix.Concat(Obj.m_formMatrix);
 
   for (FX_STRSIZE k = 0; k < nItems; k++) {
-    wchar_t wChar = actText.GetAt(k);
+    wchar_t wChar = actText[k];
     if (wChar <= 0x80 && !isprint(wChar))
       wChar = 0x20;
     if (wChar >= 0xFFFD)
@@ -1005,12 +1004,12 @@ void CPDF_TextPage::ProcessTextObject(PDFTEXT_Obj Obj) {
               pTextObj->GetFont()->UnicodeFromCharCode(item.m_CharCode);
           if (wstrItem.IsEmpty())
             wstrItem += (wchar_t)item.m_CharCode;
-          wchar_t curChar = wstrItem.GetAt(0);
+          wchar_t curChar = wstrItem[0];
           if (curChar == 0x2D || curChar == 0xAD)
             return;
         }
         while (m_TempTextBuf.GetSize() > 0 &&
-               m_TempTextBuf.AsStringC().GetAt(m_TempTextBuf.GetLength() - 1) ==
+               m_TempTextBuf.AsStringC()[m_TempTextBuf.GetLength() - 1] ==
                    0x20) {
           m_TempTextBuf.Delete(m_TempTextBuf.GetLength() - 1, 1);
           m_TempCharList.pop_back();
@@ -1053,7 +1052,7 @@ void CPDF_TextPage::ProcessTextObject(PDFTEXT_Obj Obj) {
       CFX_WideString str = m_TempTextBuf.MakeString();
       if (str.IsEmpty())
         str = m_TextBuf.AsStringC();
-      if (str.IsEmpty() || str.GetAt(str.GetLength() - 1) == TEXT_SPACE_CHAR)
+      if (str.IsEmpty() || str[str.GetLength() - 1] == TEXT_SPACE_CHAR)
         continue;
 
       float fontsize_h = pTextObj->m_TextState.GetFontSizeH();
@@ -1164,7 +1163,7 @@ void CPDF_TextPage::ProcessTextObject(PDFTEXT_Obj Obj) {
       }
       if (!bDel) {
         for (int nIndex = 0; nIndex < nTotal; nIndex++) {
-          charinfo.m_Unicode = wstrItem.GetAt(nIndex);
+          charinfo.m_Unicode = wstrItem[nIndex];
           if (charinfo.m_Unicode) {
             charinfo.m_Index = m_TextBuf.GetLength();
             m_TempTextBuf.AppendChar(charinfo.m_Unicode);
@@ -1175,8 +1174,7 @@ void CPDF_TextPage::ProcessTextObject(PDFTEXT_Obj Obj) {
         }
       } else if (i == 0) {
         CFX_WideString str = m_TempTextBuf.MakeString();
-        if (!str.IsEmpty() &&
-            str.GetAt(str.GetLength() - 1) == TEXT_SPACE_CHAR) {
+        if (!str.IsEmpty() && str[str.GetLength() - 1] == TEXT_SPACE_CHAR) {
           m_TempTextBuf.Delete(m_TempTextBuf.GetLength() - 1, 1);
           m_TempCharList.pop_back();
         }
@@ -1225,12 +1223,12 @@ bool CPDF_TextPage::IsHyphen(wchar_t curChar) {
   if (nCount < 1)
     return false;
   int nIndex = nCount - 1;
-  wchar_t wcTmp = strCurText.GetAt(nIndex);
+  wchar_t wcTmp = strCurText[nIndex];
   while (wcTmp == 0x20 && nIndex > 0 && nIndex <= nCount - 1)
-    wcTmp = strCurText.GetAt(--nIndex);
+    wcTmp = strCurText[--nIndex];
   if (0x2D == wcTmp || 0xAD == wcTmp) {
     if (--nIndex > 0) {
-      wchar_t preChar = strCurText.GetAt((nIndex));
+      wchar_t preChar = strCurText[nIndex];
       if (FXSYS_iswalpha(preChar) && FXSYS_iswalpha(curChar))
         return true;
     }
@@ -1268,7 +1266,7 @@ CPDF_TextPage::GenerateCharacter CPDF_TextPage::ProcessInsertObject(
       pObj->GetFont()->UnicodeFromCharCode(item.m_CharCode);
   if (wstrItem.IsEmpty())
     wstrItem += static_cast<wchar_t>(item.m_CharCode);
-  wchar_t curChar = wstrItem.GetAt(0);
+  wchar_t curChar = wstrItem[0];
   if (WritingMode == TextOrientation::Horizontal) {
     if (this_rect.Height() > 4.5 && prev_rect.Height() > 4.5) {
       float top = this_rect.top < prev_rect.top ? this_rect.top : prev_rect.top;
@@ -1357,7 +1355,7 @@ CPDF_TextPage::GenerateCharacter CPDF_TextPage::ProcessInsertObject(
       m_pPreTextObj->GetFont()->UnicodeFromCharCode(PrevItem.m_CharCode);
   if (PrevStr.IsEmpty())
     return GenerateCharacter::None;
-  wchar_t preChar = PrevStr.GetAt(PrevStr.GetLength() - 1);
+  wchar_t preChar = PrevStr[PrevStr.GetLength() - 1];
   CFX_Matrix matrix = pObj->GetTextMatrix();
   matrix.Concat(formMatrix);
 
diff --git a/core/fpdftext/cpdf_textpagefind.cpp b/core/fpdftext/cpdf_textpagefind.cpp
index 3c8e532a7f..55f940cad7 100644
--- a/core/fpdftext/cpdf_textpagefind.cpp
+++ b/core/fpdftext/cpdf_textpagefind.cpp
@@ -110,7 +110,7 @@ bool CPDF_TextPageFind::FindFirst(const CFX_WideString& findwhat,
   m_csFindWhatArray.clear();
   int i = 0;
   while (i < len) {
-    if (findwhatStr.GetAt(i) != ' ')
+    if (findwhatStr[i] != ' ')
       break;
     i++;
   }
@@ -150,7 +150,7 @@ bool CPDF_TextPageFind::FindNext() {
     CFX_WideString csWord = m_csFindWhatArray[iWord];
     if (csWord.IsEmpty()) {
       if (iWord == nCount - 1) {
-        wchar_t strInsert = m_strText.GetAt(nStartPos);
+        wchar_t strInsert = m_strText[nStartPos];
         if (strInsert == TEXT_LINEFEED_CHAR || strInsert == TEXT_SPACE_CHAR ||
             strInsert == TEXT_RETURN_CHAR || strInsert == 160) {
           nResultPos = nStartPos + 1;
@@ -174,16 +174,16 @@ bool CPDF_TextPageFind::FindNext() {
     bool bMatch = true;
     if (iWord != 0 && !bSpaceStart) {
       int PreResEndPos = nStartPos;
-      int curChar = csWord.GetAt(0);
+      int curChar = csWord[0];
       CFX_WideString lastWord = m_csFindWhatArray[iWord - 1];
-      int lastChar = lastWord.GetAt(lastWord.GetLength() - 1);
+      int lastChar = lastWord[lastWord.GetLength() - 1];
       if (nStartPos == nResultPos &&
           !(IsIgnoreSpaceCharacter(lastChar) ||
             IsIgnoreSpaceCharacter(curChar))) {
         bMatch = false;
       }
       for (int d = PreResEndPos; d < nResultPos; d++) {
-        wchar_t strInsert = m_strText.GetAt(d);
+        wchar_t strInsert = m_strText[d];
         if (strInsert != TEXT_LINEFEED_CHAR && strInsert != TEXT_SPACE_CHAR &&
             strInsert != TEXT_RETURN_CHAR && strInsert != 160) {
           bMatch = false;
@@ -192,7 +192,7 @@ bool CPDF_TextPageFind::FindNext() {
       }
     } else if (bSpaceStart) {
       if (nResultPos > 0) {
-        wchar_t strInsert = m_strText.GetAt(nResultPos - 1);
+        wchar_t strInsert = m_strText[nResultPos - 1];
         if (strInsert != TEXT_LINEFEED_CHAR && strInsert != TEXT_SPACE_CHAR &&
             strInsert != TEXT_RETURN_CHAR && strInsert != 160) {
           bMatch = false;
@@ -293,7 +293,7 @@ void CPDF_TextPageFind::ExtractFindWhat(const CFX_WideString& findwhat) {
     int pos = 0;
     while (pos < csWord.GetLength()) {
       CFX_WideString curStr = csWord.Mid(pos, 1);
-      wchar_t curChar = csWord.GetAt(pos);
+      wchar_t curChar = csWord[pos];
       if (IsIgnoreSpaceCharacter(curChar)) {
         if (pos > 0 && curChar == 0x2019) {
           pos++;
@@ -326,12 +326,12 @@ bool CPDF_TextPageFind::IsMatchWholeWord(const CFX_WideString& csPageText,
   int char_count = endPos - startPos + 1;
   if (char_count < 1)
     return false;
-  if (char_count == 1 && csPageText.GetAt(startPos) > 255)
+  if (char_count == 1 && csPageText[startPos] > 255)
     return true;
   if (startPos - 1 >= 0)
-    char_left = csPageText.GetAt(startPos - 1);
+    char_left = csPageText[startPos - 1];
   if (startPos + char_count < csPageText.GetLength())
-    char_right = csPageText.GetAt(startPos + char_count);
+    char_right = csPageText[startPos + char_count];
   if ((char_left > 'A' && char_left < 'a') ||
       (char_left > 'a' && char_left < 'z') ||
       (char_left > 0xfb00 && char_left < 0xfb06) || std::iswdigit(char_left) ||
@@ -348,9 +348,9 @@ bool CPDF_TextPageFind::IsMatchWholeWord(const CFX_WideString& csPageText,
     return false;
   }
   if (char_count > 0) {
-    if (std::iswdigit(char_left) && std::iswdigit(csPageText.GetAt(startPos)))
+    if (std::iswdigit(char_left) && std::iswdigit(csPageText[startPos]))
       return false;
-    if (std::iswdigit(char_right) && std::iswdigit(csPageText.GetAt(endPos)))
+    if (std::iswdigit(char_right) && std::iswdigit(csPageText[endPos]))
       return false;
   }
   return true;
@@ -386,7 +386,7 @@ CFX_WideString CPDF_TextPageFind::MakeReverse(const CFX_WideString& str) {
   str2.clear();
   int nlen = str.GetLength();
   for (int i = nlen - 1; i >= 0; i--)
-    str2 += str.GetAt(i);
+    str2 += str[i];
   return str2;
 }
 
diff --git a/core/fxcrt/cfx_bytestring.cpp b/core/fxcrt/cfx_bytestring.cpp
index 0aba3be12a..cd049dcc5d 100644
--- a/core/fxcrt/cfx_bytestring.cpp
+++ b/core/fxcrt/cfx_bytestring.cpp
@@ -518,6 +518,12 @@ void CFX_ByteString::Format(const char* pFormat, ...) {
   va_end(argList);
 }
 
+void CFX_ByteString::SetAt(FX_STRSIZE index, char c) {
+  ASSERT(index >= 0 && index < GetLength());
+  ReallocBeforeWrite(m_pData->m_nDataLength);
+  m_pData->m_String[index] = c;
+}
+
 FX_STRSIZE CFX_ByteString::Insert(FX_STRSIZE index, char ch) {
   const FX_STRSIZE cur_length = m_pData ? m_pData->m_nDataLength : 0;
   if (index != pdfium::clamp(index, 0, cur_length))
@@ -694,12 +700,6 @@ FX_STRSIZE CFX_ByteString::Replace(const CFX_ByteStringC& pOld,
   return nCount;
 }
 
-void CFX_ByteString::SetAt(FX_STRSIZE index, char c) {
-  ASSERT(index >= 0 && index < GetLength());
-  ReallocBeforeWrite(m_pData->m_nDataLength);
-  m_pData->m_String[index] = c;
-}
-
 CFX_WideString CFX_ByteString::UTF8Decode() const {
   CFX_UTF8Decoder decoder;
   for (FX_STRSIZE i = 0; i < GetLength(); i++) {
@@ -721,10 +721,10 @@ int CFX_ByteString::Compare(const CFX_ByteStringC& str) const {
   int that_len = str.GetLength();
   int min_len = this_len < that_len ? this_len : that_len;
   for (int i = 0; i < min_len; i++) {
-    if ((uint8_t)m_pData->m_String[i] < str.GetAt(i)) {
+    if ((uint8_t)m_pData->m_String[i] < str[i]) {
       return -1;
     }
-    if ((uint8_t)m_pData->m_String[i] > str.GetAt(i)) {
+    if ((uint8_t)m_pData->m_String[i] > str[i]) {
       return 1;
     }
   }
diff --git a/core/fxcrt/cfx_bytestring.h b/core/fxcrt/cfx_bytestring.h
index df31751273..3e8b6619c2 100644
--- a/core/fxcrt/cfx_bytestring.h
+++ b/core/fxcrt/cfx_bytestring.h
@@ -107,14 +107,13 @@ class CFX_ByteString {
   const CFX_ByteString& operator+=(const CFX_ByteString& str);
   const CFX_ByteString& operator+=(const CFX_ByteStringC& bstrc);
 
-  uint8_t GetAt(FX_STRSIZE index) const {
+  const CharType& operator[](const FX_STRSIZE index) const {
     ASSERT(index >= 0 && index < GetLength());
     return m_pData->m_String[index];
   }
 
-  uint8_t operator[](FX_STRSIZE index) const { return GetAt(index); }
-
   void SetAt(FX_STRSIZE index, char c);
+
   FX_STRSIZE Insert(FX_STRSIZE index, char ch);
   FX_STRSIZE InsertAtFront(char ch) { return Insert(0, ch); }
   FX_STRSIZE InsertAtBack(char ch) { return Insert(GetLength(), ch); }
diff --git a/core/fxcrt/cfx_bytestring_unittest.cpp b/core/fxcrt/cfx_bytestring_unittest.cpp
index 680a37e342..35f407f6ec 100644
--- a/core/fxcrt/cfx_bytestring_unittest.cpp
+++ b/core/fxcrt/cfx_bytestring_unittest.cpp
@@ -11,26 +11,8 @@
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/base/stl_util.h"
 
-TEST(fxcrt, ByteStringGetAt) {
-  CFX_ByteString short_string("a");
-  CFX_ByteString longer_string("abc");
-  CFX_ByteString embedded_nul_string("ab\0c", 4);
-
-#ifndef NDEBUG
-  EXPECT_DEATH({ short_string.GetAt(-1); }, ".*");
-#endif
-  EXPECT_EQ('a', short_string.GetAt(0));
-#ifndef NDEBUG
-  EXPECT_DEATH({ short_string.GetAt(1); }, ".*");
-#endif
-  EXPECT_EQ('c', longer_string.GetAt(2));
-  EXPECT_EQ('b', embedded_nul_string.GetAt(1));
-  EXPECT_EQ('\0', embedded_nul_string.GetAt(2));
-  EXPECT_EQ('c', embedded_nul_string.GetAt(3));
-}
-
-TEST(fxcrt, ByteStringOperatorSubscript) {
-  CFX_ByteString abc("abc");
+TEST(fxcrt, ByteStringElementAccess) {
+  const CFX_ByteString abc("abc");
 #ifndef NDEBUG
   EXPECT_DEATH({ abc[-1]; }, ".*");
 #endif
@@ -40,22 +22,35 @@ TEST(fxcrt, ByteStringOperatorSubscript) {
 #ifndef NDEBUG
   EXPECT_DEATH({ abc[3]; }, ".*");
 #endif
-}
 
-TEST(fxcrt, ByteStringSetAt) {
-  // CFX_ByteString includes the NUL terminator for non-empty strings.
-  CFX_ByteString abc("abc");
+  CFX_ByteString mutable_abc = abc;
+  EXPECT_EQ(abc.c_str(), mutable_abc.c_str());
+  EXPECT_EQ('a', mutable_abc[0]);
+  EXPECT_EQ('b', mutable_abc[1]);
+  EXPECT_EQ('c', mutable_abc[2]);
+  EXPECT_EQ(abc.c_str(), mutable_abc.c_str());
+
 #ifndef NDEBUG
-  EXPECT_DEATH({ abc.SetAt(-1, 'd'); }, ".*");
+  EXPECT_DEATH({ mutable_abc.SetAt(-1, 'd'); }, ".*");
+  EXPECT_EQ("abc", abc);
 #endif
-  abc.SetAt(0, 'd');
-  EXPECT_EQ("dbc", abc);
-  abc.SetAt(1, 'e');
-  EXPECT_EQ("dec", abc);
-  abc.SetAt(2, 'f');
-  EXPECT_EQ("def", abc);
+  const char* c_str = abc.c_str();
+  mutable_abc.SetAt(0, 'd');
+  EXPECT_EQ(c_str, abc.c_str());
+  EXPECT_NE(c_str, mutable_abc.c_str());
+  EXPECT_EQ("abc", abc);
+  EXPECT_EQ("dbc", mutable_abc);
+
+  mutable_abc.SetAt(1, 'e');
+  EXPECT_EQ("abc", abc);
+  EXPECT_EQ("dec", mutable_abc);
+
+  mutable_abc.SetAt(2, 'f');
+  EXPECT_EQ("abc", abc);
+  EXPECT_EQ("def", mutable_abc);
 #ifndef NDEBUG
-  EXPECT_DEATH({ abc.SetAt(3, 'g'); }, ".*");
+  EXPECT_DEATH({ mutable_abc.SetAt(3, 'g'); }, ".*");
+  EXPECT_EQ("abc", abc);
 #endif
 }
 
@@ -943,25 +938,7 @@ TEST(fxcrt, ByteStringCMid) {
   EXPECT_EQ(trailing_substring, longer_string.Mid(4, 3));
 }
 
-TEST(fxcrt, ByteStringCGetAt) {
-  CFX_ByteStringC short_string("a");
-  CFX_ByteStringC longer_string("abc");
-  CFX_ByteStringC embedded_nul_string("ab\0c", 4);
-
-#ifndef NDEBUG
-  EXPECT_DEATH({ short_string.GetAt(-1); }, ".*");
-#endif
-  EXPECT_EQ('a', static_cast<char>(short_string.GetAt(0)));
-#ifndef NDEBUG
-  EXPECT_DEATH({ short_string.GetAt(1); }, ".*");
-#endif
-  EXPECT_EQ('c', static_cast<char>(longer_string.GetAt(2)));
-  EXPECT_EQ('b', static_cast<char>(embedded_nul_string.GetAt(1)));
-  EXPECT_EQ('\0', static_cast<char>(embedded_nul_string.GetAt(2)));
-  EXPECT_EQ('c', static_cast<char>(embedded_nul_string.GetAt(3)));
-}
-
-TEST(fxcrt, ByteStringCOperatorSubscript) {
+TEST(fxcrt, ByteStringCElementAccess) {
   // CFX_ByteStringC includes the NUL terminator for non-empty strings.
   CFX_ByteStringC abc("abc");
 #ifndef NDEBUG
diff --git a/core/fxcrt/cfx_chariter.cpp b/core/fxcrt/cfx_chariter.cpp
index b726a7e484..d26dd2df8f 100644
--- a/core/fxcrt/cfx_chariter.cpp
+++ b/core/fxcrt/cfx_chariter.cpp
@@ -29,7 +29,7 @@ bool CFX_CharIter::Next(bool bPrev) {
 }
 
 wchar_t CFX_CharIter::GetChar() {
-  return m_wsText.GetAt(m_nIndex);
+  return m_wsText[m_nIndex];
 }
 
 void CFX_CharIter::SetAt(int32_t nIndex) {
diff --git a/core/fxcrt/cfx_string_c_template.h b/core/fxcrt/cfx_string_c_template.h
index bc0fe1e0a0..99948e90a0 100644
--- a/core/fxcrt/cfx_string_c_template.h
+++ b/core/fxcrt/cfx_string_c_template.h
@@ -119,12 +119,12 @@ class CFX_StringCTemplate {
   FX_STRSIZE GetLength() const { return m_Length; }
   bool IsEmpty() const { return m_Length == 0; }
 
-  UnsignedType GetAt(FX_STRSIZE index) const {
+  const UnsignedType& operator[](const FX_STRSIZE index) const {
     ASSERT(index >= 0 && index < GetLength());
     return m_Ptr.Get()[index];
   }
 
-  CharType CharAt(FX_STRSIZE index) const {
+  const CharType CharAt(const FX_STRSIZE index) const {
     ASSERT(index >= 0 && index < GetLength());
     return static_cast<CharType>(m_Ptr.Get()[index]);
   }
@@ -164,8 +164,6 @@ class CFX_StringCTemplate {
     return CFX_StringCTemplate(m_Ptr.Get() + m_Length - count, count);
   }
 
-  UnsignedType operator[](FX_STRSIZE index) const { return GetAt(index); }
-
   bool operator<(const CFX_StringCTemplate& that) const {
     int result = FXSYS_cmp(reinterpret_cast<const CharType*>(m_Ptr.Get()),
                            reinterpret_cast<const CharType*>(that.m_Ptr.Get()),
diff --git a/core/fxcrt/cfx_widestring.cpp b/core/fxcrt/cfx_widestring.cpp
index c2e1e4877d..01fc8c764e 100644
--- a/core/fxcrt/cfx_widestring.cpp
+++ b/core/fxcrt/cfx_widestring.cpp
@@ -841,12 +841,6 @@ FX_STRSIZE CFX_WideString::Replace(const CFX_WideStringC& pOld,
   return nCount;
 }
 
-void CFX_WideString::SetAt(FX_STRSIZE index, wchar_t c) {
-  ASSERT(index >= 0 && index < GetLength());
-  ReallocBeforeWrite(m_pData->m_nDataLength);
-  m_pData->m_String[index] = c;
-}
-
 // static
 CFX_WideString CFX_WideString::FromLocal(const CFX_ByteStringC& str) {
   return FromCodePage(str, 0);
@@ -886,6 +880,12 @@ CFX_WideString CFX_WideString::FromUTF16LE(const unsigned short* wstr,
   return result;
 }
 
+void CFX_WideString::SetAt(FX_STRSIZE index, wchar_t c) {
+  ASSERT(index >= 0 && index < GetLength());
+  ReallocBeforeWrite(m_pData->m_nDataLength);
+  m_pData->m_String[index] = c;
+}
+
 int CFX_WideString::Compare(const wchar_t* lpsz) const {
   if (m_pData)
     return wcscmp(m_pData->m_String, lpsz);
diff --git a/core/fxcrt/cfx_widestring.h b/core/fxcrt/cfx_widestring.h
index b49e898f32..d57e47c62f 100644
--- a/core/fxcrt/cfx_widestring.h
+++ b/core/fxcrt/cfx_widestring.h
@@ -101,13 +101,11 @@ class CFX_WideString {
 
   bool operator<(const CFX_WideString& str) const;
 
-  wchar_t GetAt(FX_STRSIZE index) const {
+  const CharType& operator[](const FX_STRSIZE index) const {
     ASSERT(index >= 0 && index < GetLength());
     return m_pData->m_String[index];
   }
 
-  wchar_t operator[](FX_STRSIZE index) const { return GetAt(index); }
-
   void SetAt(FX_STRSIZE index, wchar_t c);
 
   int Compare(const wchar_t* str) const;
diff --git a/core/fxcrt/cfx_widestring_unittest.cpp b/core/fxcrt/cfx_widestring_unittest.cpp
index a23763218d..e7206dde06 100644
--- a/core/fxcrt/cfx_widestring_unittest.cpp
+++ b/core/fxcrt/cfx_widestring_unittest.cpp
@@ -10,26 +10,8 @@
 
 #include "testing/gtest/include/gtest/gtest.h"
 
-TEST(fxcrt, WideStringGetAt) {
-  CFX_WideString short_string(L"a");
-  CFX_WideString longer_string(L"abc");
-  CFX_WideString embedded_nul_string(L"ab\0c", 4);
-
-#ifndef NDEBUG
-  EXPECT_DEATH({ short_string.GetAt(-1); }, ".*");
-#endif
-  EXPECT_EQ(L'a', short_string.GetAt(0));
-#ifndef NDEBUG
-  EXPECT_DEATH({ short_string.GetAt(1); }, ".*");
-#endif
-  EXPECT_EQ(L'c', longer_string.GetAt(2));
-  EXPECT_EQ(L'b', embedded_nul_string.GetAt(1));
-  EXPECT_EQ(L'\0', embedded_nul_string.GetAt(2));
-  EXPECT_EQ(L'c', embedded_nul_string.GetAt(3));
-}
-
-TEST(fxcrt, WideStringOperatorSubscript) {
-  CFX_WideString abc(L"abc");
+TEST(fxcrt, WideStringElementAccess) {
+  const CFX_WideString abc(L"abc");
 #ifndef NDEBUG
   EXPECT_DEATH({ abc[-1]; }, ".*");
 #endif
@@ -39,21 +21,34 @@ TEST(fxcrt, WideStringOperatorSubscript) {
 #ifndef NDEBUG
   EXPECT_DEATH({ abc[4]; }, ".*");
 #endif
-}
 
-TEST(fxcrt, WideStringSetAt) {
-  CFX_WideString abc(L"abc");
+  CFX_WideString mutable_abc = abc;
+  EXPECT_EQ(abc.c_str(), mutable_abc.c_str());
+  EXPECT_EQ(L'a', mutable_abc[0]);
+  EXPECT_EQ(L'b', mutable_abc[1]);
+  EXPECT_EQ(L'c', mutable_abc[2]);
+  EXPECT_EQ(abc.c_str(), mutable_abc.c_str());
 #ifndef NDEBUG
-  EXPECT_DEATH({ abc.SetAt(-1, L'd'); }, ".*");
+  EXPECT_DEATH({ mutable_abc.SetAt(-1, L'd'); }, ".*");
+  EXPECT_EQ(L"abc", abc);
 #endif
-  abc.SetAt(0, L'd');
-  EXPECT_EQ(L"dbc", abc);
-  abc.SetAt(1, L'e');
-  EXPECT_EQ(L"dec", abc);
-  abc.SetAt(2, L'f');
-  EXPECT_EQ(L"def", abc);
+  const wchar_t* c_str = abc.c_str();
+  mutable_abc.SetAt(0, L'd');
+  EXPECT_EQ(c_str, abc.c_str());
+  EXPECT_NE(c_str, mutable_abc.c_str());
+  EXPECT_EQ(L"abc", abc);
+  EXPECT_EQ(L"dbc", mutable_abc);
+
+  mutable_abc.SetAt(1, L'e');
+  EXPECT_EQ(L"abc", abc);
+  EXPECT_EQ(L"dec", mutable_abc);
+
+  mutable_abc.SetAt(2, L'f');
+  EXPECT_EQ(L"abc", abc);
+  EXPECT_EQ(L"def", mutable_abc);
 #ifndef NDEBUG
-  EXPECT_DEATH({ abc.SetAt(3, L'g'); }, ".*");
+  EXPECT_DEATH({ mutable_abc.SetAt(3, L'g'); }, ".*");
+  EXPECT_EQ(L"abc", abc);
 #endif
 }
 
@@ -780,25 +775,7 @@ TEST(fxcrt, WideStringCFromVector) {
   EXPECT_EQ(nullptr, cleared_string.raw_str());
 }
 
-TEST(fxcrt, WideStringCGetAt) {
-  CFX_WideStringC short_string(L"a");
-  CFX_WideStringC longer_string(L"abc");
-  CFX_WideStringC embedded_nul_string(L"ab\0c", 4);
-
-#ifndef NDEBUG
-  EXPECT_DEATH({ short_string.GetAt(-1); }, ".*");
-#endif
-  EXPECT_EQ(L'a', static_cast<wchar_t>(short_string.GetAt(0)));
-#ifndef NDEBUG
-  EXPECT_DEATH({ short_string.GetAt(1); }, ".*");
-#endif
-  EXPECT_EQ(L'c', static_cast<wchar_t>(longer_string.GetAt(2)));
-  EXPECT_EQ(L'b', static_cast<wchar_t>(embedded_nul_string.GetAt(1)));
-  EXPECT_EQ(L'\0', static_cast<wchar_t>(embedded_nul_string.GetAt(2)));
-  EXPECT_EQ(L'c', static_cast<wchar_t>(embedded_nul_string.GetAt(3)));
-}
-
-TEST(fxcrt, WideStringCOperatorSubscript) {
+TEST(fxcrt, WideStringCElementAccess) {
   CFX_WideStringC abc(L"abc");
 #ifndef NDEBUG
   EXPECT_DEATH({ abc[-1]; }, ".*");
diff --git a/core/fxcrt/xml/cxml_parser.cpp b/core/fxcrt/xml/cxml_parser.cpp
index 4d9e3dc469..ebd5873b33 100644
--- a/core/fxcrt/xml/cxml_parser.cpp
+++ b/core/fxcrt/xml/cxml_parser.cpp
@@ -171,7 +171,7 @@ void CXML_Parser::SkipLiterals(const CFX_ByteStringC& str) {
   int32_t i = 0, iLen = str.GetLength();
   do {
     while (m_dwIndex < m_dwBufferSize) {
-      if (str.GetAt(i) != m_pBuffer[m_dwIndex++]) {
+      if (str[i] != m_pBuffer[m_dwIndex++]) {
         i = 0;
         continue;
       }