---
name: "CURLOPT_MIME_OPTIONS"
section: "3"
platform: "linux"
package: "curl"
version: "8.23.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "macos"]
url: "https://new.carta.tech/CURLOPT_MIME_OPTIONS"
---

# CURLOPT\_MIME\_OPTIONS(3)

set MIME option flags

## NAME

CURLOPT\_MIME\_OPTIONS - set MIME option flags

## SYNOPSIS

```
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_MIME_OPTIONS, long options);
```

## DESCRIPTION

Pass a long that holds a bitmask of options. Each bit is a boolean flag used while encoding a MIME tree or multipart form data.

Available bits are:

- CURLMIMEOPT\_FORMESCAPE

  Tells libcurl to escape multipart form field and filenames using the backslash-escaping algorithm rather than percent-encoding (HTTP only).

  Backslash-escaping consists in preceding backslashes and double quotes with a backslash. Percent encoding maps all occurrences of double quote, carriage return and line feed to %22, %0D and %0A respectively.

  Before version 7.81.0, percent-encoding was never applied.

  HTTP browsers used to do backslash-escaping in the past but have over time transitioned to use percent-encoding. This option allows one to address server-side applications that have not yet have been converted.

  As an example, consider field or filename *strangename"kind*. When the containing multipart form is sent, this is normally transmitted as *strangename%22kind*. When this option is set, it is sent as *strangename"kind*.

## DEFAULT

0, meaning disabled.

## PROTOCOLS

This functionality affects http, imap and smtp

## EXAMPLE

```
int main(void)
{
  CURL *curl = curl_easy_init();
  curl_mime *form = NULL;
  if(curl) {
    CURLcode result = CURLE_OK;
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
    curl_easy_setopt(curl, CURLOPT_MIME_OPTIONS, CURLMIMEOPT_FORMESCAPE);
    form = curl_mime_init(curl);
    if(form) {
      curl_mimepart *part = curl_mime_addpart(form);
      if(part) {
        curl_mime_filedata(part, "strange\\file\\name");
        curl_mime_name(part, "strange\"field\"name");
        curl_easy_setopt(curl, CURLOPT_MIMEPOST, form);
        /* Perform the request */
        result = curl_easy_perform(curl);
      }
    }
    curl_easy_cleanup(curl);
    curl_mime_free(form);
  }
}
```

## HISTORY

**CURLMIMEOPT\_FORMESCAPE** macro became *long* type in 8.16.0, prior to this version a *long* cast was necessary when passed to *[curl\_easy\_setopt(3)](/curl_easy_setopt/3.md)*.

## AVAILABILITY

Added in curl 7.81.0

## RETURN VALUE

*[curl\_easy\_setopt(3)](/curl_easy_setopt/3.md)* returns a CURLcode indicating success or error.

CURLE\_OK (0) means everything was OK, non-zero means an error occurred, see *[libcurl-errors(3)](/libcurl-errors/3.md)*.

## SEE ALSO

[**CURLOPT\_HTTPPOST**(3)](/CURLOPT_HTTPPOST/3.md), [**CURLOPT\_MIMEPOST**(3)](/CURLOPT_MIMEPOST/3.md)