How to Use cURL and C to Send Emails

Fixing Email Sending Problems Using cURL and C

Writing C Code Using the cURL Library

#include <stdio.h>
#include <string.h>
#include <curl/curl.h>
#define EMAIL "email@gmail.com"
#define PASSWORD "password"
#define TO_EMAIL "to_email@example.com"
char *send_email(char *body) {
    CURL *curl;
    CURLcode res = CURLE_OK;
    struct curl_slist *recipients = ;
    curl = curl_easy_init();
    if (curl) {
        char from[100];
        sprintf(from, "From: %s", EMAIL);
        recipients = curl_slist_append(recipients, from);
        char to[100];
        sprintf(to, "To: %s", TO_EMAIL);
        recipients = curl_slist_append(recipients, to);
        recipients = curl_slist_append(recipients, "Content-Type: text/plain");
        curl_easy_setopt(curl, CURLOPT_USERNAME, EMAIL);
        curl_easy_setopt(curl, CURLOPT_PASSWORD, PASSWORD);
        curl_easy_setopt(curl, CURLOPT_URL, "smtps://smtp.gmail.com:465");
        curl_easy_setopt(curl, CURLOPT_USE_SSL, (long)CURLUSESSL_ALL);
        curl_easy_setopt(curl, CURLOPT_MAIL_FROM, EMAIL);
        curl_easy_setopt(curl, CURLOPT_MAIL_RCPT, recipients);
        curl_easy_setopt(curl, CURLOPT_READFUNCTION, );
        curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);
        curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);
        const char *message = body;
        curl_easy_setopt(curl, CURLOPT_READDATA, message);
        curl_easy_setopt(curl, CURLOPT_INFILESIZE, (long)strlen(message));
        res = curl_easy_perform(curl);
        if (res != CURLE_OK)
            fprintf(stderr, "curl_easy_perform() failed: %s\\n", curl_easy_strerror(res));
        curl_slist_free_all(recipients);
        curl_easy_cleanup(curl);
    }
    return "ok";
}

Improving cMake Configuration for Integration with cURL

CMake Configuration Script

cmake_minimum_required(VERSION 3.26)
project(aplicacao_back_end C)
set(CMAKE_C_STANDARD 11)
include_directories(lib\\libmicrohttpd\\include)
link_directories(lib\\libmicrohttpd\\lib)
set(CURL_LIBRARY "-lcurl")
include_directories(lib\\libcurl\\include)
link_directories(lib\\libcurl\\lib)
find_package(CURL REQUIRED)
add_executable(aplicacao_back_end main.c scripts/email.c scripts/email.h)
target_link_libraries(aplicacao_back_end microhttpd ws2_32 ${CURL_LIBRARIES})
# Note: Ensure that libcurl.dll is available in your system PATH or in the same directory as your executable

Email Integration FAQ

1. What does a C application employing cURL's error code -1073741515 mean?
2. This issue usually indicates that there is a missing libcurl.dll in the executable directory or system path of the application, which prevents the required DLL file from being located.
3. How should a CMake project link to cURL?
4. In your CMakeLists.txt file, you must include find_package(CURL REQUIRED) and make sure your system paths are configured properly.
5. Why, while utilizing cURL, does the program disregard breakpoints?
6. This might be the result of unhandled errors, like not initializing cURL with curl_easy_init(), causing the application to terminate prematurely.
7. What does curl_slist_append() want to achieve?
8. It is applied to a list that will be used for email sending in order to add headers or recipient emails.
9. How can I use cURL's verbose mode to debug problems?
10. Setting curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L) will activate verbose mode, which produces thorough mailing process logs.

Concluding Remarks on cURL-Based SMTP Configuration in C

It takes close attention to library setup, configuration settings, and error handling to send messages using cURL in C. The necessity of checking environment paths and dependencies to avoid typical mistakes that can impair email functionality has been brought to light by this case study. Through adherence to optimal methodologies in project setup and code execution, developers can efficiently utilize cURL for SMTP connections within their C applications, guaranteeing dependable and efficient email delivery systems.