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authorBruce Dawson <brucedawson@google.com>2014-12-08 16:19:45 -0800
committerBruce Dawson <brucedawson@google.com>2014-12-08 16:19:45 -0800
commit4429eaa2d0c5f07118a57418a469ee39461cd4c5 (patch)
treeb748c58c4ead58f65cf0d56545d7c6b38c19b3ec /core/include/fxcrt/fx_basic.h
parentb69da0b96ffdad124efd1b48d51c617bb216a98e (diff)
downloadpdfium-4429eaa2d0c5f07118a57418a469ee39461cd4c5.tar.xz
Replace manual/error-prone/hard-to-verify arraysize calculations with safe FX_ArraySize macro.
pdfium has numerous places where the number of elements in an array is calculated with expressions like: sizeof(cFormats)/sizeof(FX_LPCWSTR) This is suboptimal because it is verbose, it is easy to get wrong, and it cannot be determined through casual inspection whether the code is correct. It will give incorrect results if cFormats is a pointer instead of an array and it will give incorrect results if FX_LPCWSTR is not the type of the array elements. The FX_WSTRC macro in fx_string.h which I fixed was particularly scary because it would silently misbehave if passed a pointer. The FX_ArraySize macro which I have added and started using (taken from arraysize in v8's macros.h) is easier to use and will always give correct results. If passed a pointer it will fail to compile. For this change I only fixed instances of sizeof(FX_LPCWSTR). There appear to be about 150 other places in the pdfium code that could benefit from using FX_ArraySize. R=bo_xu@foxitsoftware.com, tsepez@chromium.org Review URL: https://codereview.chromium.org/729293003
Diffstat (limited to 'core/include/fxcrt/fx_basic.h')
-rw-r--r--core/include/fxcrt/fx_basic.h16
1 files changed, 16 insertions, 0 deletions
diff --git a/core/include/fxcrt/fx_basic.h b/core/include/fxcrt/fx_basic.h
index 22ba611a77..98a540c455 100644
--- a/core/include/fxcrt/fx_basic.h
+++ b/core/include/fxcrt/fx_basic.h
@@ -18,6 +18,22 @@
#ifndef _FX_STREAM_H_
#include "fx_stream.h"
#endif
+
+// The FX_ArraySize(arr) macro returns the # of elements in an array arr.
+// The expression is a compile-time constant, and therefore can be
+// used in defining new arrays, for example. If you use FX_ArraySize on
+// a pointer by mistake, you will get a compile-time error.
+//
+// One caveat is that FX_ArraySize() doesn't accept any array of an
+// anonymous type or a type defined inside a function.
+#define FX_ArraySize(array) (sizeof(ArraySizeHelper(array)))
+
+// This template function declaration is used in defining FX_ArraySize.
+// Note that the function doesn't need an implementation, as we only
+// use its type.
+template <typename T, size_t N>
+char (&ArraySizeHelper(T (&array)[N]))[N];
+
class CFX_BinaryBuf : public CFX_Object
{
public: