CODEWITHSUNDEEP
cmemory-managementmalloc
Szabolcs
Szabolcs

Reputation: 25703

Compatibility of free/malloc between compilers

Suppose I have a library compiled with compiler A. It allocates memory using malloc() and leaves it to me to free() it. It provides no special free function.

Can I compile my program (that uses this library) with compiler B? Or do I have to worry that one compiler's (standard library's) malloc is incompatible with the other's free?

In addition to the general question I would also like to know the answer specifically for these compilers: system clang on OS X with MacPorts' gcc 4.9 or 5.

Upvotes: 4

Views: 942

Answers (2)

Barmar
Barmar

Reputation: 781096

It shouldn't be a problem. The operating system's ABI specifies how programs call library functions, and all programs and libraries are supposed to conform to this. This allows you to link programs created with different compilers together.

Your question indicates a confusion between compilers and libraries. Compiling a library with compiler A doesn't mean it uses Library A's malloc function. Libraries are specified during the link step, not when compiling the library. When you create the executable program, you link the main program with the library you compiled and the C runtime library. malloc and free are provided in the C runtime library, and there will just be one of them in the resulting executable.

Upvotes: 4

Szabolcs
Szabolcs

Reputation: 25703

free and malloc are not always compatible between compilers. Specifically, they are not compatible between MSVC and MinGW.

I encountered the following situation:

I was using a C library that has a function that returns an array. The array must be freed by the user when no longer needed. I was using a precompiled DLL of this library using MSVC. However, the DLL was compiled with MinGW. Using MSVC's free on memory that was allocated with MinGW's malloc causes a crash. But ensuring that free/malloc are always used in compatible pairs avoided the trouble, even if my program used a different C compiler than the DLL.

Upvotes: 3

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