C语言 在 C 中，如何使用 libcurl 将 HTTP 响应读入字符串？
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In C, how do you use libcurl to read a HTTP response into a string?
提问by empty set
I have homework where I need somehow to compare two HTTP responses. I am writing it on C and I use libcurl to make things easier. I am calling the function that uses libcurl to do a HTTP request and response from another function, and I want to return the HTTP response as a char *. Here is my code so far (it crashes):
我有作业需要以某种方式比较两个 HTTP 响应。我在 C 上写它，我使用 libcurl 使事情变得更容易。我正在调用使用 libcurl 执行来自另一个函数的 HTTP 请求和响应的函数，并且我想将 HTTP 响应作为char *. 到目前为止，这是我的代码（它崩溃了）：
#include <stdio.h>
#include <curl/curl.h>
#include <string.h>
size_t write_data(void *ptr, size_t size, size_t nmemb, void *stream) {
size_t written;
written = fwrite(ptr, size, nmemb, stream);
return written;
}
char *handle_url(void) {
CURL *curl;
char *fp;
CURLcode res;
char *url = "http://www.yahoo.com";
curl = curl_easy_init();
if (curl) {
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);
if(res != CURLE_OK)
fprintf(stderr, "curl_easy_perform() failed: %s\n", curl_easy_strerror(res));
curl_easy_cleanup(curl);
//printf("\n%s", fp);
}
return fp;
}
This solution C libcurl get output into a stringworks, but not in my case because I just want to return the string to the calling function.
这个解决方案C libcurl get output into a string有效，但在我的情况下不是，因为我只想将字符串返回给调用函数。
Any ideas?
有任何想法吗？
回答by mpontillo
Fixed it for you. You need to handle the case where the write_data()function is called multiple times, and pass it the right kind of parameter. You also need to keep track of how big a structure you've got, so you can allocate enough memory.
给你修好了。您需要处理write_data()多次调用该函数的情况，并向其传递正确类型的参数。您还需要跟踪您拥有的结构有多大，以便分配足够的内存。
I left in a debug printfin the write_datafunction to help you understand how it works.
我在函数中进行了调试printf，write_data以帮助您了解它是如何工作的。
#include <stdio.h>
#include <curl/curl.h>
#include <string.h>
#include <stdlib.h>
struct url_data {
size_t size;
char* data;
};
size_t write_data(void *ptr, size_t size, size_t nmemb, struct url_data *data) {
size_t index = data->size;
size_t n = (size * nmemb);
char* tmp;
data->size += (size * nmemb);
#ifdef DEBUG
fprintf(stderr, "data at %p size=%ld nmemb=%ld\n", ptr, size, nmemb);
#endif
tmp = realloc(data->data, data->size + 1); /* +1 for '##代码##' */
if(tmp) {
data->data = tmp;
} else {
if(data->data) {
free(data->data);
}
fprintf(stderr, "Failed to allocate memory.\n");
return 0;
}
memcpy((data->data + index), ptr, n);
data->data[data->size] = '##代码##';
return size * nmemb;
}
char *handle_url(char* url) {
CURL *curl;
struct url_data data;
data.size = 0;
data.data = malloc(4096); /* reasonable size initial buffer */
if(NULL == data.data) {
fprintf(stderr, "Failed to allocate memory.\n");
return NULL;
}
data.data[0] = '##代码##';
CURLcode res;
curl = curl_easy_init();
if (curl) {
curl_easy_setopt(curl, CURLOPT_URL, url);
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);
curl_easy_setopt(curl, CURLOPT_WRITEDATA, &data);
res = curl_easy_perform(curl);
if(res != CURLE_OK) {
fprintf(stderr, "curl_easy_perform() failed: %s\n",
curl_easy_strerror(res));
}
curl_easy_cleanup(curl);
}
return data.data;
}
int main(int argc, char* argv[]) {
char* data;
if(argc < 2) {
fprintf(stderr, "Must provide URL to fetch.\n");
return 1;
}
data = handle_url(argv[1]);
if(data) {
printf("%s\n", data);
free(data);
}
return 0;
}
Note: compile with gcc -o test test.c -lcurl(assuming you pasted into test.c). Use gcc -o test test.c -lcurl -DDEBUGto see the test printf()calls.
注意：编译gcc -o test test.c -lcurl（假设您粘贴到test.c）。使用gcc -o test test.c -lcurl -DDEBUG查看测试printf()呼叫。
Disclaimer: this is ugly, quick-and-dirty code. There may be bugs. Please see the more robust, better commented example here.
免责声明：这是丑陋、快速和肮脏的代码。可能有bug。请在此处查看更强大、评论更好的示例。
