Program crashes on line t->time = t0;

Question

I am usiung MinGW as my c programing environment, but I found a serious problem. My test code is as follows:

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

typedef struct {        /* time struct */
    time_t time;        /* time (s) expressed by standard time_t */
    double sec;         /* fraction of second under 1 s */
} gtime_t;

typedef struct {       
    gtime_t time;        
    int type;         
} raw_t;

int main(){
    raw_t *t;
    gtime_t t0={0};
    t->time = t0;
    printf ("%d",(t->time).time);

    return 0;
}

I defined two struct and one struct is contained in the other one. When I run this test program, it will crush on line

t->time = t0;

Can someone help me on this?

when copying a struct, a simple assignment will (usually) not do the job. Suggest: `memcpy( &t->time, &to, sizeof( gtime_t ) ); — user3629249, Oct 15 '15 at 05:34
the `double` format has an offset in the exponent, so initializing to {0} will not result in a value that is 0.0. Suggest reading" which contains: "The double-precision binary floating-point exponent is encoded using an offset-binary representation, with the zero offset being 1023; also known as exponent bias in the IEEE 754 standard" — user3629249, Oct 15 '15 at 05:45

Phuong Nguyen · Answer 1 · 2015-10-16T01:57:08.130

3

t is a pointer that has not been initialized. So you can't dereferenced it to assign value to member. You can either initialize it by heap

t = malloc(sizeof(raw_t));

Or initialize by stack

raw_t tonthestack;
raw_t *t = &tonthestack;

edited Oct 16 '15 at 01:57

answered Oct 15 '15 at 03:19

Phuong Nguyen

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[don't cast the result of `malloc` in C](http://stackoverflow.com/q/605845/995714) – phuclv Oct 15 '15 at 04:02

score 1 · Answer 2 · answered Oct 15 '15 at 03:20

1

Your code uses an uninitalized pointer:

raw_t *t;
t->time =

You must make t point somewhere before you are allowed to write t->.

A simpler solution would be to not use a pointer at all:

raw_t t = { 0 };
printf("%d\n", t.time.time);

answered Oct 15 '15 at 03:20

M.M

138,810
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Program crashes on line t->time = t0;

2 Answers2