libdarwin/h/stdio.h

   1 /*
   2  * Copyright (c) 2018 Apple Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. Please obtain a copy of the License at
  10  * http://www.opensource.apple.com/apsl/ and read it before using this
  11  * file.
  12  *
  13  * The Original Code and all software distributed under the License are
  14  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  15  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  16  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  18  * Please see the License for the specific language governing rights and
  19  * limitations under the License.
  20  *
  21  * @APPLE_LICENSE_HEADER_END@
  22  */
  23
  24 /*!
  25  * @header
  26  * Non-standard, Darwin-specific additions for the stdio(3) family of APIs.
  27  */
  28 #ifndef __DARWIN_STDIO_H
  29 #define __DARWIN_STDIO_H
  30
  31 #include <os/base.h>
  32 #include <os/api.h>
  33 #include <sys/cdefs.h>
  34
  35 __BEGIN_DECLS;
  36
  37 /*!
  38  * @function zsnprintf_np
  39  * snprintf(3) variant which returns the numnber of bytes written less the null
  40  * terminator.
  41  *
  42  * @param buff
  43  * The buffer in which to write the string.
  44  *
  45  * @param len
  46  * The length of the buffer.
  47  *
  48  * @param fmt
  49  * The printf(3)-like format string.
  50  *
  51  * @param ...
  52  * The arguments corresponding to the format string.
  53  *
  54  * @result
  55  * The number of bytes written into the buffer, less the null terminator. This
  56  * routine is useful for successive string printing that may be lossy, as it
  57  * will simply return zero when there is no space left in the destination
  58  * buffer, i.e. enables the following pattern:
  59  *
  60  * char *cur = buff;
  61  * size_t left = sizeof(buff);
  62  * for (i = 0; i < n_strings; i++) {
  63  *     size_t n_written = zsnprintf_np(buff, left, "%s", strings[i]);
  64  *     cur += n_written;
  65  *     left -= n_written;
  66  * }
  67  *
  68  * This loop will safely terminate without any special care since, as soon as
  69  * the buffer's space is exhausted, all further calls to zsnprintf_np() will
  70  * write nothing and return zero.
  71  */
  72 DARWIN_API_AVAILABLE_20170407
  73 OS_EXPORT OS_WARN_RESULT OS_NONNULL1 OS_NONNULL3 OS_FORMAT_PRINTF(3, 4)
  74 size_t
  75 zsnprintf_np(char *buff, size_t len, const char *fmt, ...);
  76
  77 __END_DECLS;
  78
  79 #endif // __DARWIN_STDIO_H