Returning strings with const char * in C [duplicate]

Question

I'm trying to understand why the following string passing works for my error string. I have made this example from a much bigger source I have.

My question is; why don't I have to specifically allocate memory for the char array which contains my error message? I would have thought that I need to malloc some memory for the string and use the err pointer to indicate the start of this memory.

Is this to do with that fact that its a const char * or is is because I'm printing to stderr?

I'm possibly wording the question wrong which is why searches haven't helped me to understand this.

const char * my_function(int a)
{
     if (a != 1)
         return "a doesn't equal 1!"
     else
         return NULL;

}

int main(int a)
{
    const char *err;
    err = my_function(a);
    if (err)
         fprintf(stderr, "Message = %s\n",err);
         return 1;
    return 0;
}

Answer 1

All string literals are allocated at compile time. They already reside in a read-only section of the program memory when your program is started; they aren't allocated in runtime. You can regard them as constant character arrays. And like any const variable, they remain valid throughout the whole execution of the program.

Answer 2

String literals are allocated as const char arrays with static storage duration, so they live for the entire lifetime of the program. The scope they happen to be in is irrelevant -- they always have static storage duration.

That means you can take their address (which happen implicitly if you return a string literal or store it in a const char * variable anywhere) without having to worry about the lifetime of the resulting pointer. The storage for the string literal will never be used for something else.