libc/src/stdio/printf_core/strerror_converter.h

   1 //===-- Strerror Converter for printf ---------------------------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef LLVM_LIBC_SRC_STDIO_PRINTF_CORE_STRERROR_CONVERTER_H
  10 #define LLVM_LIBC_SRC_STDIO_PRINTF_CORE_STRERROR_CONVERTER_H
  11
  12 #include "src/__support/StringUtil/error_to_string.h"
  13 #include "src/__support/macros/config.h"
  14 #include "src/stdio/printf_core/core_structs.h"
  15 #include "src/stdio/printf_core/int_converter.h"
  16 #include "src/stdio/printf_core/string_converter.h"
  17 #include "src/stdio/printf_core/writer.h"
  18
  19 namespace LIBC_NAMESPACE_DECL {
  20 namespace printf_core {
  21
  22 LIBC_INLINE int convert_strerror(Writer *writer, const FormatSection &to_conv) {
  23   FormatSection new_conv = to_conv;
  24   const int error_num = static_cast<int>(to_conv.conv_val_raw);
  25
  26   // The %m conversion takes no arguments passes the result of strerror(errno)
  27   // to a string conversion (including all options). If the alternate form flag
  28   // is set, then if errno is a valid error number the string of the errno macro
  29   // is passed to a string conversion, else the integer value of errno is passed
  30   // to an integer conversion.
  31
  32   // It's assumed that errno is passed in to_conv.conv_val_raw.
  33
  34   // normal form
  35   if ((to_conv.flags & FormatFlags::ALTERNATE_FORM) == 0) {
  36     char strerror_buff[64];
  37     auto strerror_result = get_error_string(error_num, strerror_buff);
  38     new_conv.conv_val_ptr =
  39         reinterpret_cast<void *>(const_cast<char *>(strerror_result.data()));
  40     new_conv.conv_name = 's';
  41     return convert_string(writer, new_conv);
  42   } else {
  43     // alt form
  44
  45     // The handling of errno = 0 is in alt form weird. The rule for %m in alt
  46     // form is "named macros print their name, else print errno as int." There
  47     // isn't a specific name for errno = 0, but it does have an explicit meaning
  48     // (success). Due to the way the string mappings work, it's easiest to just
  49     // say that 0 is a valid macro with a string of "0". This works fine for
  50     // most cases, but for precision and the int flags it changes the behavior.
  51     // Given that this behavior is so incredibly deep in the weeds I doubt
  52     // anyone would notice, I'm going to leave it as the simplest to implement
  53     // (0 maps to "0"), which also happens to match what other libc
  54     // implementations have done.
  55
  56     auto errno_name = try_get_errno_name(error_num);
  57     // if there's a name available, use it.
  58     if (errno_name) {
  59       new_conv.conv_val_ptr =
  60           reinterpret_cast<void *>(const_cast<char *>(errno_name->data()));
  61       new_conv.conv_name = 's';
  62       return convert_string(writer, new_conv);
  63     } else {
  64       // else do an int conversion
  65       new_conv.conv_name = 'd';
  66       return convert_int(writer, new_conv);
  67     }
  68   }
  69 }
  70
  71 } // namespace printf_core
  72 } // namespace LIBC_NAMESPACE_DECL
  73
  74 #endif // LLVM_LIBC_SRC_STDIO_PRINTF_CORE_STRERROR_CONVERTER_H