warning: comparison between pointer and integer in C

问题

I get a warning

warning: comparison between pointer and integer

on the line containing if from the next piece of code:

char cwd[1024];

if (getcwd(cwd, sizeof(cwd)) != (char*)NULL)
    printf("%s\n",cwd);
else
    error_print("error in pwd");

how and what do I need to fix?

回答1:

Do you include unistd.h? If not, the error appears because your C compiler is assuming getcwd returns int.

The fix? Include unistd.h

回答2:

The prototype of getcwd is

char *getcwd(char *buf, size_t size);

Make sure you include <unistd.h> otherwise the return type would default to int.

Here, even Ideone gives its Current Working Directory

回答3:

have you included the .h necessary so that the compiler understands what getcwd returns?

the behavior of your c compilers is probably to assume an int return value from every undefined function.

回答4:

In the return types section of the following link, getcwd returns null on failure. Thus, instead of checking for != (char *)NULL just check for != NULL

http://linux.die.net/man/3/getcwd

回答5:

Modify line with this one if (getcwd(cwd, sizeof(cwd)) != NULL)

来源：https://stackoverflow.com/questions/5654685/warning-comparison-between-pointer-and-integer-in-c