C：比较两个字符数组

Question

C : compare two character arrays

Here's my rot function

int my_rot13(int c) {
    if ('a' <= tolower(c) && tolower(c) <= 'z')
        return tolower(c)+13 <= 'z' ? c+13 : c-13;
    return c;
}

int my_rot13cmp(char *a, char *b) {
    int i;
    for (i=1; i<strlen(a); i++) {
        if (my_rot13(a[i]) > my_rot13(b[i])) {
            return 1;
        }
    }
    return -1;
}

And this should output 1 because D will be Q in decoded character W will be J in decoded character And Q > J

printf("%d \n", my_rot13cmp("\0D\n", "\0W\n"));

But this keeps giving me -1

What is the correct way to compare these two characters?

Answer 1

You have an embedded 0 character in your strings:

 my_rot13cmp("\0D\n", "\0W\n");

This will cause strlen(a) inside my_rot13cmp to return 0 - since a nul character means the end of the string.

Remove those \\0 in your strings, and start the loop at i=0

Answer 2

strlen looks for \\0 symbol to determine string length, your strings has this special symbol, so strlen will not work, you have several variants:

1 have separate argument for length, like:

int my_rot13cmp(char *a, char *b, size_t aLength, size_t bLength)
{
    if (aLength > bLength)
        return 1;
    if (aLength < bLength)
        return -1;
    for (int i=0; i<aLength; i++)
        if (my_rot13(a[i]) > my_rot13(b[i]))
            return 1;
        else if (my_rot13(a[i]) < my_rot13(b[i]))
            return -1;
    return 0;
}

2 if you know that all your strings just started with \\0 and do not contain it until the end (asciiz null terminator must be), you can go with this solution:

int my_rot13cmp(char *a, char *b)
{
    a++; b++; // skips first \0 symbol
    for (int i=0; i<strlen(a); i++) // note: what will be if A is longer than B?
        if (my_rot13(a[i]) > my_rot13(b[i]))
            return 1;
        else if (my_rot13(a[i]) < my_rot13(b[i]))
            return -1;
    return 0;
}