difference between and

Question

When I use malloc in a C program, I get a warning:

warning: incompatible implicit declaration of built-in function \'malloc\' [enabled by defaul         


        

Answer 1

The header is deprecated (and quite Linux specific, on which it defines non-standard functions like mallinfo(3)). Use instead if you simply need malloc(3) and related standard functions (e.g. free, calloc, realloc ....). Notice that is defined by C89 (and later) standards, but not

Look into /usr/include/malloc.h you'll find there some non-standard functions (e.g. malloc_stats(3), etc...) - in addition of malloc....

And gcc don't link header files, but libraries. Read Levine's book about linkers & loaders for more.

If you don't include any headers (and dont explicitly declare malloc yourself, which would be a bad idea), malloc is implicitly declared as returning some int value (which is wrong). I do invite you to pass at least the -Wall flag to gcc when using it.

You might also pass -v to gcc to understand the actual programs involved: cc1 is the compiler proper (producing assembly code), as the assembler, ld the linker, and collect2 an internal utility which invokes the linker.