libc/src/__support/CPP/stringstream.h

   1 //===-- A simple implementation of string stream class ----------*- 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___SUPPORT_CPP_STRINGSTREAM_H
  10 #define LLVM_LIBC_SRC___SUPPORT_CPP_STRINGSTREAM_H
  11
  12 #include "span.h"
  13 #include "src/__support/macros/config.h"
  14 #include "string_view.h"
  15 #include "type_traits.h"
  16
  17 #include "src/__support/integer_to_string.h"
  18
  19 namespace LIBC_NAMESPACE_DECL {
  20 namespace cpp {
  21
  22 // This class is to be used to write simple strings into a user provided buffer
  23 // without any dynamic memory allocation. There is no requirement to mimic the
  24 // C++ standard library class std::stringstream.
  25 class StringStream {
  26   span<char> data;
  27   size_t write_ptr = 0; // The current write pointer
  28   bool err = false;     // If an error occurs while writing
  29
  30   void write(const char *bytes, size_t size) {
  31     size_t i = 0;
  32     const size_t data_size = data.size();
  33     for (; write_ptr < data_size && i < size; ++i, ++write_ptr)
  34       data[write_ptr] = bytes[i];
  35     if (i < size) {
  36       // If some of the characters couldn't be written, set error.
  37       err = true;
  38     }
  39   }
  40
  41 public:
  42   static constexpr char ENDS = '\0';
  43
  44   // Create a string stream which will write into |buf|.
  45   constexpr StringStream(const span<char> &buf) : data(buf) {}
  46
  47   // Return a string_view to the current characters in the stream. If a
  48   // null terminator was not explicitly written, then the return value
  49   // will not include one. In order to produce a string_view to a null
  50   // terminated string, write ENDS explicitly.
  51   string_view str() const { return string_view(data.data(), write_ptr); }
  52
  53   // Write the characters from |str| to the stream.
  54   StringStream &operator<<(string_view str) {
  55     write(str.data(), str.size());
  56     return *this;
  57   }
  58
  59   // Write the |val| as string.
  60   template <typename T, enable_if_t<is_integral_v<T>, int> = 0>
  61   StringStream &operator<<(T val) {
  62     const IntegerToString<T> buffer(val);
  63     return *this << buffer.view();
  64   }
  65
  66   template <typename T, enable_if_t<is_floating_point_v<T>, int> = 0>
  67   StringStream &operator<<(T) {
  68     // If this specialization gets activated, then the static_assert will
  69     // trigger a compile error about missing floating point number support.
  70     static_assert(!is_floating_point_v<T>,
  71                   "Writing floating point numbers is not yet supported");
  72     return *this;
  73   }
  74
  75   // Write a null-terminated string. The terminating null character is not
  76   // written to allow stremaing to continue.
  77   StringStream &operator<<(const char *str) {
  78     return operator<<(string_view(str));
  79   }
  80
  81   // Write a single character.
  82   StringStream &operator<<(char a) {
  83     write(&a, 1);
  84     return *this;
  85   }
  86
  87   // Return true if any write operation(s) failed due to insufficient size.
  88   bool overflow() const { return err; }
  89
  90   size_t bufsize() const { return data.size(); }
  91 };
  92
  93 } // namespace cpp
  94 } // namespace LIBC_NAMESPACE_DECL
  95
  96 #endif // LLVM_LIBC_SRC___SUPPORT_CPP_STRINGSTREAM_H