CURLOPT_WRITEDATA(3) curl_easy_setopt options CURLOPT_WRITEDATA(3)NAME
CURLOPT_WRITEDATA - custom pointer passed to the write callback
SYNOPSIS
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_WRITEDATA, void *pointer);
DESCRIPTION
A data pointer to pass to the write callback. If you use the CURLOPT_WRITEFUNCTION(3) option, this is the pointer you'll get in that call-
back's 4th argument. If you don't use a write callback, you must make pointer a 'FILE *' (cast to 'void *') as libcurl will pass this to
fwrite(3) when writing data.
The internal CURLOPT_WRITEFUNCTION(3) will write the data to the FILE * given with this option, or to stdout if this option hasn't been
set.
If you're using libcurl as a win32 DLL, you MUST use the CURLOPT_WRITEFUNCTION(3) if you set this option or you will experience crashes.
DEFAULT
By default, this is a FILE * to stdout.
PROTOCOLS
Used for all protocols.
EXAMPLE
A common technique is to use the write callback to store the incoming data into a dynamically growing allocated buffer, and then this CUR-
LOPT_WRITEDATA(3) is used to point to a struct or the buffer to store data in. Like in the getinmemory example:
https://curl.haxx.se/libcurl/c/getinmemory.html
AVAILABILITY
Available in all libcurl versions. This option was formerly known as CURLOPT_FILE, the name CURLOPT_WRITEDATA(3) was introduced in 7.9.7.
RETURN VALUE
This will return CURLE_OK.
SEE ALSO CURLOPT_WRITEFUNCTION(3), CURLOPT_READDATA(3),
libcurl 7.54.0 February 03, 2016 CURLOPT_WRITEDATA(3)
Check Out this Related Man Page
CURLOPT_HEADERFUNCTION(3) curl_easy_setopt options CURLOPT_HEADERFUNCTION(3)NAME
CURLOPT_HEADERFUNCTION - callback that receives header data
SYNOPSIS
#include <curl/curl.h>
size_t header_callback(char *buffer,
size_t size,
size_t nitems,
void *userdata);
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HEADERFUNCTION, header_callback);
DESCRIPTION
Pass a pointer to your callback function, which should match the prototype shown above.
This function gets called by libcurl as soon as it has received header data. The header callback will be called once for each header and
only complete header lines are passed on to the callback. Parsing headers is very easy using this. The size of the data pointed to by buf-
fer is size multiplied with nmemb. Do not assume that the header line is zero terminated! The pointer named userdata is the one you set
with the CURLOPT_HEADERDATA(3) option. This callback function must return the number of bytes actually taken care of. If that amount dif-
fers from the amount passed in to your function, it'll signal an error to the library. This will cause the transfer to get aborted and the
libcurl function in progress will return CURLE_WRITE_ERROR.
A complete HTTP header that is passed to this function can be up to CURL_MAX_HTTP_HEADER (100K) bytes.
If this option is not set, or if it is set to NULL, but CURLOPT_HEADERDATA(3) is set to anything but NULL, the function used to accept
response data will be used instead. That is, it will be the function specified with CURLOPT_WRITEFUNCTION(3), or if it is not specified or
NULL - the default, stream-writing function.
It's important to note that the callback will be invoked for the headers of all responses received after initiating a request and not just
the final response. This includes all responses which occur during authentication negotiation. If you need to operate on only the headers
from the final response, you will need to collect headers in the callback yourself and use HTTP status lines, for example, to delimit
response boundaries.
When a server sends a chunked encoded transfer, it may contain a trailer. That trailer is identical to a HTTP header and if such a trailer
is received it is passed to the application using this callback as well. There are several ways to detect it being a trailer and not an
ordinary header: 1) it comes after the response-body. 2) it comes after the final header line (CR LF) 3) a Trailer: header among the regu-
lar response-headers mention what header(s) to expect in the trailer.
For non-HTTP protocols like FTP, POP3, IMAP and SMTP this function will get called with the server responses to the commands that libcurl
sends.
DEFAULT
Nothing.
PROTOCOLS
Used for all protocols with headers or meta-data concept: HTTP, FTP, POP3, IMAP, SMTP and more.
EXAMPLE
static size_t header_callback(char *buffer, size_t size,
size_t nitems, void *userdata)
{
/* received header is nitems * size long in 'buffer' NOT ZERO TERMINATED */
/* 'userdata' is set with CURLOPT_HEADERDATA */
return nitems * size;
}
CURL *curl = curl_easy_init();
if(curl) {
curl_easy_setopt(curl, CURLOPT_URL, "http://example.com");
curl_easy_setopt(curl, CURLOPT_HEADERFUNCTION, header_callback);
curl_easy_perform(curl);
}
AVAILABILITY
Always
RETURN VALUE
Returns CURLE_OK
SEE ALSO CURLOPT_HEADERDATA(3), CURLOPT_WRITEFUNCTION(3),
libcurl 7.54.0 February 03, 2016 CURLOPT_HEADERFUNCTION(3)