char *find_path(char **envp) {
    if (envp = NULL || *envp = NULL)
        return 0;
    while (ft_strncmp("PATH=", *envp, 5))
        envp  ; 
    return (*envp   5);
}

I tried envp to be zero, also tried comparing string of PATH not found in envp (environmental variable) using strcmp but it causes the segmentation fault.

I want to test if we unset the PATH, I want to return the function as normal and not cause a segmentation fault.

CodePudding user response：

Please format your code before posting; it's difficult to read when it's weirdly indented like that.

To check for equality in C, you must use ==, not =. = will set envp to NULL and return its new value. Since this value is 0, the if clause will be evaluated to false and return 0 won't execute. Also, you should have tested what happens if envp isn't 0 before assuming that's the problem. Your code fragment causes a segmentation fault no matter what value envp is entering the function, since it's changed to NULL anyways.

char *find_path(char **envp)
{
    if (envp == NULL)
        return 0;
    if (*envp == NULL)
        return 0;
    while(ft_strncmp("PATH=", *envp, 5))
        envp  ; 
    return (*envp   5);
}

CodePudding user response：

Aside from the typo in the first if statement (both = should be ==), which is probably a mistake copying your code into the question, it should be clear that if

    while(ft_strncmp("PATH=", *envp, 5)) envp  ;

doesn't find PATH= in the environment, it will reach the NULL terminator at the end of the envp array, which it will then dereference (and blow up).

CodePudding user response：

There are multiple problems:

• bad indentation: it made the code hard to read for both you and the next programmer. Your school might enforce local coding style rules by giving a fail mark (0) for badly indented code.

• the tests envp = NULL and *envp = NULL are incorrect: the = operator sets envp to NULL and this evaluated to false, then || attempts to set *envp to NULL, causing the segmentation fault as *envp is now a null pointer. You should use == instead of =

• The while loop does not have a proper ending condition: if envp reaches the end of the environ array, *envp will be a null pointer, potentially causing ft_strncmp to crash (depending if it tests for null pointers or not). You should iterate while the *envp is non null and return *envp 5 if the comparison returns 0. This removes the need for the second initial test.

Here is a modified version:

char *find_path(char **envp) {
    if (envp) {
        while (*envp) {
            if (ft_strncmp("PATH=", *envp, 5) == 0)
                return *envp   5;
            envp  ;
        }
    }
    // no environment or PATH not found: return a null pointer
    return 0;
}