String version of challenge

Objective-C Programming (2nd Edition) 9. Addresses and Pointers
1

I decided to conduct a version of the challenge using strings. Here is my code:

//
// main.c
// Addresses
//
// Created by Keith Jones on 8/13/14.
// Copyright © 2014 Keith Jones. All rights reserved.
//

#include <stdio.h>
#include <stdlib.h>

int main(int argc, const char * argv[])
{

char *str = "Hi Mom";
printf("String = %s\n", str);
printf("Length of string is %zu\n", sizeof("Hi Mom"));
printf("Length of string is %zu\n", sizeof(str));
printf("Length of string is %zu\n\n", sizeof(*str));

return EXIT_SUCCESS;

}

Here is the resultant output:

String = Hi Mom
Length of string is 7
Length of string is 8
Length of string is 1

Program ended with exit code: 0

I found this result odd. My hypothesis is that
printf(“Length of string is %zu\n”, sizeof(“Hi Mom”)); counts the characters in the string not including a string termination character
printf(“Length of string is %zu\n”, sizeof(str)); counts the number of characters in the string plus a string termination character
printf(“Length of string is %zu\n\n”, sizeof(*str)); counts only the first character in the string

I don’t know that there is a string termination character. I am inferring that there is because it would be necessary to identify the end of the string when the string is referenced by pointer. When the string is a constant string, the termination character would not be necessary since the end of the string is deterministic. I am correct or way off base? Any alternate explanations of the results of this experiment?

thanks

2

Use the strlen function, not the sizeof operator, to get the length of a C string.

3

Thank you.

Modified code

printf("String = %s\n", str);
printf("Length of string is %zu\n", sizeof("Hi Mom"));
printf("Length of string is %zu\n", sizeof(str));

printf(“Length of string is %zu\n”, strlen(“Hi Mom”));
printf(“Length of string is %zu\n”, strlen(str));
printf(“Length of string is %zu\n\n”, sizeof(*str));

New output

String = Hi Mom
Length of string is 7
Length of string is 8
Length of string is 6
Length of string is 6
Length of string is 1

Program ended with exit code: 0

Any idea how to interpret the results when I mistakenly used sizeof and why they’re different when I pass a constant string compared to passing a pointer to the string?

Thanks again