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The use of type-generic function-like macros is an allowed exception (PRE00-EX4) to PRE00-C. Prefer inline or static functions to function-like macros.
Exception
When compiling a 64-bit application on an LP64 or LLP64 platform, this recommendation should not be used because it is possible for the cast to hide a bug. If stdlib.h is not properly included, the compiler will assume the declaration of malloc() to be int malloc(). When sizeof(int) on the platform is 4, the resulting pointer could be truncated due to the compiler assuming malloc() returns a 32-bit integer. Additionally, casting the results of malloc() to a pointer on these platforms can also sign extend a negative 32-bit integer to an invalid pointer.
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|---|---|---|---|---|
| ||||
/* #include <stdlib.h> is missing */
int main() {
int i;
for (i = 0; i < 100; ++i) {
char *ptr = (char*)malloc(0x10000000); /* int malloc() assumed */
*ptr = 'a';
}
return 0;
}
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On an LLP64/LP64 platform, such as Microsoft Windows, the above code will eventually cause an access violation when dereferencing ptr in the loop.
Risk Assessment
Failing to cast the result of a memory allocation function call into a pointer to the allocated type can result in inadvertent pointer conversions. Code that follows this recommendation will compile and execute equally well in C++.
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