从URL下载一个文件到C++的磁盘

Question

I have a simple question. Is it possible to write simple code to download a file from the inte.net (from URL to disk) without using C++ (for mac osx) libraries like curl? I have seen some examples but all of these use the Curl library.

i use this code on my xcode projet..but i have some compilation (linking) errors

    #define CURL_STATICLIB
#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;
    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] = "bbb.txt";
    curl = curl_easy_init();
    if (curl) {
        fp = fopen(outfilename,"wb");
        curl_easy_setopt(curl, CURLOPT_URL, url);
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp);
        res = curl_easy_perform(curl);
        curl_easy_cleanup(curl);
        fclose(fp);
    }
    return 0;
}

how can i link the curl library to my xcode project?

Answer 1

You can launch a console command, it is very simple:D

system("curl -o ...")

or

system("wget ...")

Answer 2

You have to learn bits of "socket programming" and implement a very basic HTTP protocol; the minimalist thing is to send string like "GET /this/path/to/file.png HTTP/1.0\r\n" to the site; then, likely it will answer with an HTTP header you have to parse to know at least the length of the binary data following (if the request succeeded, otherwise you have to handle HTTP errors, or a unexpected contet-type like a html page).

This guide should give you the basic to start with; about HTTP , it depends on your need, sometimes sending a "raw" GET could suffice, sometimes not.

EDIT

Changed to pretend that the request comes from a HTTP/1 compliant client, since HTTP/1.1 wants the Host header to be sent, as commenter has rightly pointed.

EDIT2

The OP changed the question, which became something about how to link with a library in Xcode. There's already a similar question on SO .

Answer 3

"Downloading a file from URL" means basically doing an GET request to some remote HTTP server. So you need to have your application know how to do that HTTP request.

But HTTP is now a quite complex protocol. Its specification alone is long and complex (more than a hundred pages). libcurl is a good library implementing it.

Why do you want to avoid using a good free library implementing a complex protocol? Of course, you could implement the complex HTTP protocol by yourself (probably that needs years of work), or make a minimal program which don't implement all the details of HTTP protocol but might work (but won't work with weird HTTP servers).