asked on

Do i have to allocate and free memory

Do i have to allocate and free memory for path in the following program, and why?

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>

int main()
{
char *path;

path = getenv("PATH");

printf("Current path = ", path);
}

ASKER CERTIFIED SOLUTION

zebada

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F. Dominicus

Well you better make a copy of the returned string. If you do this

path = getenv("SOME_VAR");

some computation
and than

path1 = getenv("SOME_OTHER_VAR);

you will lost the content of path. So the "right" thing to do is makeing a copy of value returned by getenv.

Regards
Friedrich

zebada

No that's not right.
getenv() returns a different address fro each different environment variable.

F. Dominicus

You are right. It seems I have messed that up with some other function.

Regards
Friedrich

BackupName

ASKER

How do I recognize functions that return memory that is allocated/deallocated by the operating system. Can you show me an example of other functions that work this way? And thanks.

zebada

You ned to read the documentation to understand return values and how they may be used.

Off the top of my head I do not know of any other functions that work like getenv().

Anyone else know?

F. Dominicus

Well the only thing that really helps is a up-to-date documentation. Anyway therea are some hints that memory allocation is around if there is a some sort of "free" function. Example is fopen and fclose, open and close
malloc and free ;-), regfree.

I do not know any Standard C function which do require an explicitly free after usage. You just have to be careful about extern libraries. Which anyway should state their requirements very clearly.

Regards
Friedrich