Add CFX_ByteStringC::CharAt() to avoid c_str() and casts.

Most of the time, we want to operate on chars as if they
were unsigned, but there are a few places where we need
the default (questionably signed) values. Consolidate
the casting in a single place rather than forcing callers
to get a char* ptr.

BUG=pdfium:493

Review-Url: https://codereview.chromium.org/1972053003

3 files changed, 7 insertions, 8 deletions

diff --git a/core/fpdfapi/fpdf_font/cpdf_font.cpp b/core/fpdfapi/fpdf_font/cpdf_font.cpp
index f143bed541..9fb54a828b 100644
--- a/core/fpdfapi/fpdf_font/cpdf_font.cpp
+++ b/core/fpdfapi/fpdf_font/cpdf_font.cpp
@@ -149,7 +149,7 @@ FX_BOOL CPDF_Font::IsVertWriting() const {
 }
 
 int CPDF_Font::AppendChar(FX_CHAR* buf, uint32_t charcode) const {
-  *buf = (FX_CHAR)charcode;
+  *buf = static_cast<FX_CHAR>(charcode);
   return 1;
 }
 
diff --git a/core/fpdfapi/fpdf_font/fpdf_font.cpp b/core/fpdfapi/fpdf_font/fpdf_font.cpp
index dccce5656b..9f7b127d60 100644
--- a/core/fpdfapi/fpdf_font/fpdf_font.cpp
+++ b/core/fpdfapi/fpdf_font/fpdf_font.cpp
@@ -139,12 +139,12 @@ uint32_t CPDF_ToUnicodeMap::StringToCode(const CFX_ByteStringC& str) {
   int result = 0;
   if (str[0] == '<') {
     for (int i = 1; i < len && std::isxdigit(str[i]); ++i)
-      result = result * 16 + FXSYS_toHexDigit(str[i]);
+      result = result * 16 + FXSYS_toHexDigit(str.CharAt(i));
     return result;
   }
 
   for (int i = 0; i < len && std::isdigit(str[i]); ++i)
-    result = result * 10 + FXSYS_toDecimalDigit(static_cast<FX_CHAR>(str[i]));
+    result = result * 10 + FXSYS_toDecimalDigit(str.CharAt(i));
 
   return result;
 }
diff --git a/core/fpdfapi/fpdf_parser/fpdf_parser_utility.cpp b/core/fpdfapi/fpdf_parser/fpdf_parser_utility.cpp
index 03975149b0..1e9252fa82 100644
--- a/core/fpdfapi/fpdf_parser/fpdf_parser_utility.cpp
+++ b/core/fpdfapi/fpdf_parser/fpdf_parser_utility.cpp
@@ -87,21 +87,20 @@ int32_t GetDirectInteger(CPDF_Dictionary* pDict, const CFX_ByteStringC& key) {
 }
 
 CFX_ByteString PDF_NameDecode(const CFX_ByteStringC& bstr) {
-  int size = bstr.GetLength();
-  const FX_CHAR* pSrc = bstr.c_str();
   if (bstr.Find('#') == -1)
     return bstr;
 
+  int size = bstr.GetLength();
   CFX_ByteString result;
   FX_CHAR* pDestStart = result.GetBuffer(size);
   FX_CHAR* pDest = pDestStart;
   for (int i = 0; i < size; i++) {
-    if (pSrc[i] == '#' && i < size - 2) {
+    if (bstr[i] == '#' && i < size - 2) {
       *pDest++ =
-          FXSYS_toHexDigit(pSrc[i + 1]) * 16 + FXSYS_toHexDigit(pSrc[i + 2]);
+          FXSYS_toHexDigit(bstr[i + 1]) * 16 + FXSYS_toHexDigit(bstr[i + 2]);
       i += 2;
     } else {
-      *pDest++ = pSrc[i];
+      *pDest++ = bstr[i];
     }
   }
   result.ReleaseBuffer((FX_STRSIZE)(pDest - pDestStart));