\0 doesn't print the number next to it-CodePudding

I found this trick/problem on the web and would like to understand what's happening.

#include <stdio.h>
#include <string.h>

int main(){
    char s[] = "S\0C5AB";
    printf("%s", s);
    printf("%d", sizeof(s)); // 7
    printf("  -- %d", strlen(s)); // 1
}

Everything worked as expected.

But when put a number after \0 sizeof and strlen both ignore \0 and the number next to it.

int main(){
    char s[] = "S\065AB";
    printf("%s   ", s); // S5AB
    printf("--- %d", sizeof(s)); // 5
    printf("  -- %d", strlen(s)); // 4
}

Link to the above code: https://godbolt.org/z/7qfYq51E4

What's happening here?

CodePudding user response：

C provides for 1, 2 or 3 octal digits to be specified within a string.

In the first string char s[] = "S\0C5AB"; the single digit after the backslash is compiled to the value 0.

This definition is equivalent to:

char s[] = { 'S', 0, 'C', '5', 'A', 'B', '\0' }; // 0 == '\0'. They are the same

The second example posted contains 3 octal digits in sequence, and 065 == ASCII '5'

This means the 2nd example (char s[] = "S\065AB";) is an array like this:

char s[] = { 'S', '5', 'A', 'B', '\0' }; // \065 ==> '5'