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23 .TH CURLOPT_WRITEFUNCTION 3 "February 03, 2016" "libcurl 7.59.0" "curl_easy_setopt options"
26 CURLOPT_WRITEFUNCTION \- set callback for writing received data
29 #include <curl/curl.h>
31 size_t write_callback(char *ptr, size_t size, size_t nmemb, void *userdata);
33 CURLcode curl_easy_setopt(CURL *handle, CURLOPT_WRITEFUNCTION, write_callback);
35 Pass a pointer to your callback function, which should match the prototype
38 This callback function gets called by libcurl as soon as there is data
39 received that needs to be saved. \fIptr\fP points to the delivered data, and
40 the size of that data is \fIsize\fP multiplied with \fInmemb\fP.
42 The callback function will be passed as much data as possible in all invokes,
43 but you must not make any assumptions. It may be one byte, it may be
44 thousands. The maximum amount of body data that will be passed to the write
45 callback is defined in the curl.h header file: \fICURL_MAX_WRITE_SIZE\fP (the
46 usual default is 16K). If \fICURLOPT_HEADER(3)\fP is enabled, which makes
47 header data get passed to the write callback, you can get up to
48 \fICURL_MAX_HTTP_HEADER\fP bytes of header data passed into it. This usually
51 This function may be called with zero bytes data if the transferred file is
54 The data passed to this function will not be zero terminated!
56 Set the \fIuserdata\fP argument with the \fICURLOPT_WRITEDATA(3)\fP option.
58 Your callback should return the number of bytes actually taken care of. If
59 that amount differs from the amount passed to your callback function, it'll
60 signal an error condition to the library. This will cause the transfer to get
61 aborted and the libcurl function used will return \fICURLE_WRITE_ERROR\fP.
63 If your callback function returns CURL_WRITEFUNC_PAUSE it will cause this
64 transfer to become paused. See \fIcurl_easy_pause(3)\fP for further details.
66 Set this option to NULL to get the internal default function used instead of
67 your callback. The internal default function will write the data to the FILE *
68 given with \fICURLOPT_WRITEDATA(3)\fP.
70 libcurl will use 'fwrite' as a callback by default.
74 Support for the CURL_WRITEFUNC_PAUSE return code was added in version 7.18.0.
76 This will return CURLE_OK.
78 A common technique is to use this callback to store the incoming data into a
79 dynamically growing allocated buffer. Like in the getinmemory example:
80 https://curl.haxx.se/libcurl/c/getinmemory.html
82 .BR CURLOPT_WRITEDATA "(3), " CURLOPT_READFUNCTION "(3), "