指向打印 null 的字符串的指针数组

Question

I'm learning C in a restricted OS (xv6) that only has a subset of C. I'm trying split a single string into an array of strings.

To do that, I've constructed an array of pointers to strings lines . My expectation is that lines will end up looking like this: lines = { "abc", "def", "ghi" }

When I try to access lines by index (eg lines[0]) I'm getting null . I'm stumped why I'm getting null and have tried several things. I'm pretty sure I'm missing something very obvious.

Note: Not looking for working code, as I would like to continue building this myself, but would appreciate some guidance on why I'm getting this result.

#define STDIN 0
#define STDOUT 1

static void readline(){
    char buff[] = "abc\ndef\nghi";
    int i,j;
    char current[20];
    char *lines[20];
    int counter = -1;
    int lines_counter = -1;
    for(i = 0; i < 14; i++) {
        if(buff[i] == '\n' || buff[i] == '\0'){
            lines_counter++;
            for(j = 0; j < 4; j++) {
                lines[lines_counter][j] = current[j];
            }
            counter = -1;
        } else {
          current[++counter] = buff[i];
        }
    }
    printf(STDOUT, "%s", lines[0]); // expected "aaa", instead output is(null)
}

int main(int argc, char *argv[]) {
    readline(); 
    exit();
}

Answer 1

I would advise just looking at the source code of strtok and try expanding any standard library calls. strchr is just a search for a char in a string and strcspn just counts the number of characters before strchr returns.