强制函数返回 NULL 而不是预先确定的 return_type

Question

Below is a command parsing function. It splits user input at the "-" .

If "time-10" is passed in, 10 is returned. If no "-" is found I want to return NULL so I know that no "-" was found and the program can make decisions passed on that information. However, because the function return type is char I have to return a char pointer, and am currently satisfying this requirement by returning the original argument.

Is there a way around this, or do I HAVE to return a Char pointer and write code that determines if that return value equates to, 'no - found' ?

char * second_arg(char * arg) {  
    char * j = strchr(arg, '-');
    if(j==NULL) {
        return arg;
    }
    return ++j;
}

Answer 1

The function return type is not char ; it is char * . Since the function already returns a pointer to char , it is very easy to return NULL.

Just change the line return arg; to say return NULL;

Answer 2

Tim Randall posted the right answer. A little code-golf oriented solution could also be:

char * second_arg(char * arg) {  
    char * j = strchr(arg, '-');
    return j?++j:j;
}

If j is NULL , it's also false in C. ++j increments the variable before the evaluation of the line (I suggest to add comments to this code :)).