CODEWITHSUNDEEP
carrayspointersmallocsizeof
Black_Zero
Black_Zero

Reputation: 465

Wrong size in dynamic memory allocation

I am puzzled by the output of this code:

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

#define TIMING_OUTPUT_FILENAME_MAX_LENGTH 40

    int main (int argc, char **argv)
    {
        char *timing_output_filename = malloc(TIMING_OUTPUT_FILENAME_MAX_LENGTH);
        printf("requested buffer size is %ld bytes and pointer size is %ld bytes\n", 
        sizeof(timing_output_filename),
        sizeof(*timing_output_filename));

        return 0;
    }

and here is the output:

requested buffer size is 8 bytes and pointer size is 1 bytes

It's supposed to return me 40 bytes? Am I missing something?

Upvotes: 0

Views: 263

Answers (1)

Sourav Ghosh
Sourav Ghosh

Reputation: 134286

It's supposed to return me 40 bytes?

No, it's not.

In your code, timing_output_filename is a pointer and using sizeof operator on a pointer yields the size of the pointer itself, not the size of the allocated memory (to the pointer).

In your code, sizeof(timing_output_filename) is the same as sizeof(char *), so it produces the size of a pointer to char as in your platform.

Note: sizeof produces a result of type size_t, so you should use %zu format specifier to print the result.

Upvotes: 5

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