Different array sizes

Question

When I run the following program, I get different array sizes. I tired different ways but the result is the same, what could io be doing wrong ?

#include<stdio.h>

void array_size(char *a[])
{
    printf("Func Array Size: %d\n", sizeof(a));
}

int main()
{
    char *str_array[]={"one", "two", "three"};

    printf("Array Size: %d\n", (int)sizeof(str_array));

    array_size(str_array);

    return 0;
}

From C99 you can use the `"%zu"` to correctly print a `size_t`value. — effeffe, Apr 25 '13 at 13:08

score 1 · Answer 1 · answered Apr 25 '13 at 13:04

In function main str_array is an array with three char *.

The parameter a of function array_size is just a pointer. The compiler does not dynamically pass array length information when calling array_size.

The size of one pointer is not equal the size of three char * pointers.

score -1 · Answer 2 · answered Apr 25 '13 at 13:03

-1

This is because sizeof is a compiler built-in and not a runtime function. It is hard-coded into the binary.

`sizeof((char *)[]) = sizeof(a) = sizeof(void *)`
`sizeof(str_array) = sizeof({"one", "two", "three"}) = 3 * sizeof(char *)`

answered Apr 25 '13 at 13:03

Sergey L.

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That's not the issue. Also, it's not guaranteed that `sizeof(char **) == `sizeof(void *)`. – Fred Foo Apr 25 '13 at 13:04

Different array sizes

2 Answers2