How to use libcurl in qt ?

ankit thakar

I followed all the steps mentioned in above link though I am getting undefined reference to _imp__cur

My question is do I need to build libcurl source code manually and create dlls which can be used in my project ? Can't I use the binaries which are available in [https://curl.se/download.html] ?

jsulm

@ankit-thakar C libraries are less problematic - you can use a build for your platform.
C++ libraries though require that they are built using same compiler (for example you can't mix MSVC and MinGW).

ankit thakar

@jsulm :- Which means I need to build libcurl code using mingw and then I need to use those generated binaries in my application, right ?

One more question is performance wise is libcurl better or QNetworkAccessManager ?
Let's say if I want to download some files from jenkins server which one will be better ?

jsulm

@ankit-thakar said in How to use libcurl in qt ?:

Which means I need to build libcurl code using mingw

Actually not, as libcurl is a C library as far as I know.
What is faster I don't know.

Can you post your build log with the error and also your pro file?

ankit thakar

Actually when I used Qt 5.13.2 mintgw environment it is working but unfortunately my program crashes in curl_easy_perform API.

Below is my .pro file

QT -= gui
TARGET = MyCurl
CONFIG += c++11 console
CONFIG -= app_bundle


DEFINES += QT_DEPRECATED_WARNINGS



SOURCES += \
        main.cpp

LIBS+=D:/curl-7.84.0_4-win64-mingw/curl-7.84.0_4-win64-mingw/lib/libcurl.a
LIBS+=D:/curl-7.84.0_4-win64-mingw/curl-7.84.0_4-win64-mingw/lib/libcurl.dll.a

INCLUDEPATH += D:/curl-7.84.0_4-win64-mingw/curl-7.84.0_4-win64-mingw/include

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

here is my main.cpp


#include <stdio.h>
#include <curl/curl.h>
#include <QDebug>
#include <string>
int main(void)
{
    CURL *curl;
    FILE *fp;
    CURLcode res;
    std::string url = "https://upload.wikimedia.org/wikipedia/commons/thumb/3/31/Nusfjord_road%2C_2010_09.jpg/1280px-Nusfjord_road%2C_2010_09.jpg";

   
    char outfilename[FILENAME_MAX] = "D:/ankit.jpg";
    curl = curl_easy_init();
    if (curl)
    {
        fp = fopen(outfilename,"wb");
        curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
        curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0L);
        //curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0L);
        //curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, NULL);
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp);
        res = curl_easy_perform(curl);

        if(res == CURLE_OK)
            printf("Download Successful.");
        else
            printf("Not sucessful");

        curl_easy_cleanup(curl);
        fclose(fp);
    }
    return 0;
}

jsulm

@ankit-thakar said in How to use libcurl in qt ?:

my program crashes in curl_easy_perform API

Please post the stack trace after the crash

ankit thakar

ChrisW67

Make this:

char outfilename[FILENAME_MAX] = "D:/ankit.jpg";

a Windows path:

char outfilename[FILENAME_MAX] = "D:\\ankit.jpg";

The code crashes on my Linux box because fp is null after the file could not be created.

PS: Always check the result of operations that can fail, especially those returning pointers.

ankit thakar

@ChrisW67 Actually the problem was something else, in libcurl documentation it is mentioned that callback function if you are using win32 dll.

static size_t cb(void *data, size_t size, size_t nmemb, void *userp)
{
   FILE *fp = (FILE*)userp;
   return fwrite(data, size, nmemb, fp);
}

        curl_easy_setopt(handles[i], CURLOPT_WRITEFUNCTION, cb);
        curl_easy_setopt(handles[i], CURLOPT_WRITEDATA, fp);

please refer link text