C program for downloading files with curl

Question

I am trying to write a program in C to download some files.

The source code:

#include <stdio.h>
#include <string.h>
#include <curl/curl.h>
#include <curl/easy.h>

size_t write_data(void *ptr, size_t size, size_t nmemb, FILE *stream) {
    size_t written;
    written = fwrite(ptr, size, nmemb, stream);
    return written;
}

int main(){

    if(curl_global_init(CURL_GLOBAL_ALL)){
        printf("curl error. Exiting.\n");
        return 1;
    }
    char links[3][100] = {
        "http://download.freeroms.com/nes_roms/08/big_nose_the_caveman.zip",
        "http://download.freeroms.com/nes_roms/02/contra.zip",
        "http://download.freeroms.com/nes_roms/08/super_mario_bros._(usajapan).zip"};
    int n = 0, k = 0;
    char *lastslash;
    char* name;

    CURL *handle = curl_easy_init();
    CURLcode res;
    FILE *file;

    while(n<3){
        lastslash = strrchr(links[n], '/');
        name = lastslash ? lastslash + 1 : links[n];
        printf("\nURL: %s\n", links[n]);
        printf("Filename: %s\n", name);

        curl_easy_setopt(handle, CURLOPT_URL, links[n]);
        curl_easy_setopt(handle, CURLOPT_WRITEDATA, file);
        curl_easy_setopt(handle, CURLOPT_WRITEFUNCTION, write_data);

        file = fopen(name, "wb");       
        res = curl_easy_perform(handle);

        fclose(file);
        n++;
    }

    curl_easy_cleanup(handle);
    return 0;
}

I can compile it, but this is the output when I run it :

URL: http://download.freeroms.com/nes_roms/08/big_nose_the_caveman.zip
Filename: big_nose_the_caveman.zip
Segmentation fault (core dumped)

My compiler setting:

gcc dl.c -lcurl -o dl

I found out that the problem occurs when it tries to execute curl_easy_perform(), but I don't know what to do with it.

Answer 1

try this coding.

#include <stdio.h>
#include <curl/curl.h>
#include <curl/types.h>
#include <curl/easy.h>
#include <string>

size_t write_data(void *ptr, size_t size, size_t nmemb, FILE *stream) {
    size_t written = fwrite(ptr, size, nmemb, stream);
    return written;
}

int main(void) {
    CURL *curl;
    FILE *fp;
    CURLcode res;
    char *url = "http://localhost/aaa.txt";
    char outfilename[FILENAME_MAX] = "C:\\bbb.txt";
    curl = curl_easy_init();
    if (curl) {
        fp = fopen(outfilename,"wb");
        curl_easy_setopt(curl, CURLOPT_URL, "http://localhost/aaa.txt");
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp);
        res = curl_easy_perform(curl);
        /* always cleanup */
        curl_easy_cleanup(curl);
        fclose(fp);
    }
    return 0;
}

Answer 2

You need to open the file before you set the callback data. The FILE* is stored by value, not reference.

    file = fopen(name, "wb");       
    curl_easy_setopt(handle, CURLOPT_WRITEDATA, file);