Problems with return values of function pointers

Question

I have the following SSCCE:

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

#define streq(x, y) (strcmp((x), (y)) == 0)
#define ARRAY_SIZE(x) (sizeof(x)/sizeof(x[0]))

typedef struct
{
    const char *cmd;
    void* (*fn)(void);
} __attribute__((__packed__)) Command;

void* getTime(void)
{
    return ((void*)((uintptr_t)time(NULL)));
}

void* getDay(void)
{
    time_t t = time(NULL);
    struct tm tm = *localtime(&t);
    return ((void*)((uintptr_t)(tm.tm_wday)));
}

static Command commands[] =
{
    {"time", getTime},
    {"day", getDay},
};

int main(int argc, char *argv[])
{
    for (int i = 0; i < ARRAY_SIZE(commands); ++i)
    {
        Command *p = commands+i;
        if (streq(argv[1], p->cmd)) printf("%d\n", (int)p->fn);
    }
}

My question is why when I run the code as such:

./test day

The return value is 3648 and not a value from 0-6 as specified here.

nobody · Accepted Answer · 2014-06-12 23:11:29Z

3

You need to call the function. Right now you're just printing the function pointer value. The following code should do it:

if (streq(argv[1], p->cmd)) printf("%d\n", (int)(p->fn()));

answered Jun 12, 2014 at 23:11

nobody

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1 Comment

syb0rg Over a year ago

I knew it had to be something simple that I was overlooking. Thank you!

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