Assume I have the following program:
#include <stdio.h>
int main () {
FILE * pFile;
pFile = fopen ("myfile.txt","r");
fclose (pFile);
//This never happens: free(pFile)
return 0;
}
I have never seen a program which does free(pFile)
after closing the file handle. Why is that?
I know that since fclose()
doesn't receive a pointer to pFile
, then it doesn't actually free the pointer's memory. I was under the impression that pointers should always have their memory freed if they are pointing to dynamically allocated memory. Why doesn't anyone free()
the file pointer?
free
is called in response to malloc
to return allocated memory. fopen
likely indeed does do some mallocing, but the act of closing the handle (fclose
) is, by design, going to clean up everything fopen
did. The contract you have with fopen
is that closing the handle will free all outstanding resources.
The general rule of thumb is for every alloc
have a free
. If you call a function which does an alloc
, it's description should warn you of what the caller is responsible for freeing.
Long story short, fclose
will clean up any resources created by fopen
.
Memory allocation of the fopen
function is implementation dependent (per CRT). You can be sure that fclose
is always implemented to free all the memory that fopen
allocated.
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