Why do I get a false "array subscript is above array bounds" warning message when compiling my MEX file with GCC on MATLAB 7.10 (R2010a)?

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MathWorks Support Team
When I compile the following code:
typedef struct {
int chunks[3];
} S;
void f(int y[])
{
int nc;
int i = 0;
for (nc = 0; nc < 3; nc = nc + 1) {
i = i + 1;
}
if (i < 3) {
y[i] = 0;
}
}
int main(void)
{
S tmp;
f(tmp.chunks);
return 0;
}
with this command:
gcc -Wall -O3 s3.c
I get the following warning message:
s3.c: In function 'main':
s3.c:15: warning: array subscript is above array bounds

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采纳的回答

MathWorks Support Team
This is a bug in GCC 4.3.4. For more information on this, please see the following webpage:
<http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43949>
GCC 4.4.3 has this bug fixed.
This is a false warning, and can be ignored. The -O3 switch inlines the function f() within the function main(). Now, when analyzing the inlined code, the compiler knows that y has 3 elements. However, it failes to consider the fact that on line 15, i is guaranteed to be less than 3 by the condition on line 14, so out of bounds subscript is not possible.
If the -Werror switch is specified, the warning is treated as an error, and the compilation will fail.
To work around this issue, you can either:
1. Compile the code with the –Wno-array-bounds switch
2. If in a header file, add the following code fragment to the header
// suppress bogus warning when compiling with gcc 4.3
#if (__GNUC__ == 4 && __GNUC_MINOR__ == 3)
#pragma GCC diagnostic ignored "-Warray-bounds"
#endif

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