Dangerous Code (C/C++)
Posted: Thu Oct 02 2008
Some coding practices can cause problems in release and/or debug builds and pass unnoticed by the compiler. The code itself is NOT problematic but missing a semi-colon can cause problems while compiling correctly.
For example:
Case 1:
Case 2:
Looking at the definition of AGL_ASSERT
If we miss a semi-colon after AGL_ASSERT, the problems arise and what we see is NOT what we get at runtime.
In case 1, if _DEBUG_GLIB_TRACE is not defined (in release mode), the statement_2 after the AGL_ASSERT gets executed when A is false.
In case 2, if _DEBUG_GLIB_TRACE IS defined, statement_3 is executed if C is true AND D is true:
So my recommendation is to never #define anything as an empty statement or define it as a series of statements without enclosing it between curly brackets, we can easily get a troublesome code.
I would use the following definition for AGL_ASSERT
NB. As for the do {;} while(0), the compiler would optimize the code and remove it safely from the binary.
For example:
Case 1:
Code: Select all
if (A)
statement_1;
else
AGL_ASSERT(B);
statement_2;Code: Select all
If (C)
AGL_ASSERT(D);
Else
statement_3;Code: Select all
#ifdef _DEBUG_GLIB_TRACE
#define AGL_ASSERT(x) if (!(x)) AGL_CrtDbgBreak();
#else
#define AGL_ASSERT(x)In case 1, if _DEBUG_GLIB_TRACE is not defined (in release mode), the statement_2 after the AGL_ASSERT gets executed when A is false.
In case 2, if _DEBUG_GLIB_TRACE IS defined, statement_3 is executed if C is true AND D is true:
Code: Select all
If (C)
if (!(D))
AGL_CrtDbgBreak();
else
statement_3;I would use the following definition for AGL_ASSERT
Code: Select all
#ifdef _DEBUG_GLIB_TRACE
#define AGL_ASSERT(x) { if (!(x)) AGL_CrtDbgBreak(); }
#else
#define AGL_ASSERT(x) do {;} while(0)