C程序：getenv在GDB / DDD中返回NULL

Question

I try to call getenv in my C code, this can return correct env string in terminal, while it returns NULL in GDB/DDD.

void main() {
  char * a = getenv("ANCHOR_STEM");
  if (strlen(a)>0)
    printf("%s\n", a);
}

The GDB/DDD is started from the same terminal. Even I "show environment", this env exists.

Anyone any idea?

OS/Tools version info: RHEL Linux hostname1 2.6.32-754.3.5.el6.x86_64 #1 SMP Thu Aug 9 11:56:22 EDT 2018 x86_64 GNU/Linux GNU gdb (GDB) 7.12 gcc (GCC) 6.3.0

Answer 1

include proper header files

#include <stdlib.h>
#include <string.h>
#include <stdio.h>

Treat warning as error.

Answer 2

Even I "show environment", this env exists.

When GDB invokes your program, it starts a new shell to run this program in.

When the environment changes for the target program, most often this is the result of your shell initialization file ( ~/.bashrc , ~/.kshrc , etc.) changing the environment.

It is a really bad idea to change environment for non-interactive shells. Documentation on how to avoid it.

Answer 3

If getenv returns NULL it is because it does not find the environment variable. but still you have to be careful. This instruction if (strlen(a)>0) becomes illegal, if getenv(....) , fails. getenv sends back NULL and this instruction crash the program. It's better to test the validity of the pointer before to execute this line if (strlen(a)>0) -> which is not necessarily useful.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main() {
    char * a = getenv("ANCHOR_STEM");
    if( NULL != a ){
        (void)puts(a);
        return EXIT_SUCCESS;
    }
    (void)puts("none");
    return EXIT_FAILURE;
}