segmentation fault (malloc struct)

Question

Sorry for asking this question, I have tried to find the solution on stackoverflow, but no satisfying result. My code is as the following, thanks for your patience.

#include <inttypes.h>
#include <stdlib.h>
#include <malloc.h>
#include <memory.h>
#include <string.h>

typedef uint32_t req_id_t;
typedef uint32_t view_id_t;
typedef uint64_t db_key_type;

typedef struct view_stamp_t {
    view_id_t view_id;
    req_id_t req_id;
}view_stamp;

typedef struct consensus_component_t {
    view_stamp* highest_committed_vs;
}consensus_component;

uint64_t vstol(view_stamp* vs) {
    uint64_t result = ((uint64_t)vs->req_id)&0xFFFFFFFFl;
    uint64_t temp = (uint64_t)vs->view_id&0xFFFFFFFFl;
    result += temp<<32;
    return result;
}

int main() {
    consensus_component* comp = (consensus_component*)malloc(sizeof(consensus_component));
    memset(comp, 0, sizeof(consensus_component));
    if(NULL != comp) {
        comp->highest_committed_vs->view_id = 1;
        comp->highest_committed_vs->req_id = 0;
        db_key_type start = vstol(comp->highest_committed_vs)+1;
        printf("%" PRIu64 "\n", start);
    }
    return 0;
}

`malloc()` cast need you don't. – Iharob Al Asimi Jan 10 '16 at 16:16 — Iharob Al Asimi, Jan 10 '16 at 16:16

Iharob Al Asimi · Accepted Answer · 2016-01-10T16:18:58.170

6

You never allocate space for comp->highest_committed_vs and you check comp for NULL after dereferencing it. Try like this

int main() 
{
    consensus_component *comp = malloc(sizeof(consensus_component));
    if (comp == NULL)
        return -1;
    memset(comp, 0, sizeof(consensus_component));
    comp->highest_committed_vs = malloc(sizeof(*comp->highest_committed_vs));
    if (comp->highest_committed_vs == NULL)
    {
        free(comp);
        return -1;
    }

    comp->highest_committed_vs->view_id = 1; 
    comp->highest_committed_vs->req_id = 0;

    db_key_type start = vstol(comp->highest_committed_vs)+1;
    printf("%" PRIu64 "\n", start);

    return 0;
}

edited Jan 10 '16 at 16:18

answered Jan 10 '16 at 16:17

Iharob Al Asimi

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It even should be `NULL` after the memset, hence it's quite a reliable segfault. – dhke Jan 10 '16 at 16:18
Many thanks for your answer. I fixed it by adding `comp->highest_committed_vs = (view_stamp*)malloc(sizeof(view_stamp))` – HuangJie Jan 10 '16 at 16:24
@HuangJie Please remove the *cast* for `malloc()`, [see this](http://stackoverflow.com/a/605858/1983495). – Iharob Al Asimi Jan 10 '16 at 16:25

segmentation fault (malloc struct)

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