c - Size of char pointer array from function

Question

Using this code:

#include <stdio.h>

void printSize(char *messages[]) {
    printf("%d", sizeof(messages) / sizeof(char *));
}

int main(void) {

    printf("Size when through passing direct to function: ");
    printSize((char *[]){"Zero", "One", "Two", "Three"});
    printf("
");

    printf("Size when calculating in main: %d
", sizeof((char *[]){"Zero", "One", "Two", "Three"}) / sizeof(char *));

    return 1;
}

I get output:

Size when through passing direct to function: 1
Size when calculating in main: 4

I understand there is no way to get the correct amount of elements in a char* array, but I am curious as to why they are giving different results.

Answer 1

1. It's because char *messages[] is just syntactic sugar for char **messages, so you're just getting the size of a pointer, not the size of your whole array.

2. You can't, without passing the size along as another parameter.

You should check out the comp.lang.c FAQ section on Arrays & Pointers.