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 "string_view.h"
  13 #include "span.h"
  14 #include "type_traits.h"
  15
  16 #include "src/__support/integer_to_string.h"
  17
  18 namespace __llvm_libc {
  19 namespace cpp {
  20
  21 // This class is to be used to write simple strings into a user provided buffer
  22 // without any dynamic memory allocation. There is no requirement to mimic the
  23 // C++ standard library class std::stringstream.
  24 class StringStream {
  25   span<char> data;
  26   size_t write_ptr = 0; // The current write pointer
  27   bool err = false;     // If an error occurs while writing
  28
  29   void write(const char *bytes, size_t size) {
  30     size_t i = 0;
  31     const size_t data_size = data.size();
  32     for (; write_ptr < data_size && i < size; ++i, ++write_ptr)
  33       data[write_ptr] = bytes[i];
  34     if (i < size) {
  35       // If some of the characters couldn't be written, set error.
  36       err = true;
  37     }
  38   }
  39
  40 public:
  41   static constexpr char ENDS = '\0';
  42
  43   // Create a string stream which will write into |buf|.
  44   constexpr StringStream(const span<char> &buf) : data(buf) {}
  45
  46   // Return a string_view to the current characters in the stream. If a
  47   // null terminator was not explicitly written, then the return value
  48   // will not include one. In order to produce a string_view to a null
  49   // terminated string, write ENDS explicitly.
  50   string_view str() const { return string_view(data.data(), write_ptr); }
  51
  52   // Write the characters from |str| to the stream.
  53   StringStream &operator<<(string_view str) {
  54     write(str.data(), str.size());
  55     return *this;
  56   }
  57
  58   // Write the |val| as string.
  59   template <typename T, enable_if_t<is_integral_v<T>, int> = 0>
  60   StringStream &operator<<(T val) {
  61     char buffer[IntegerToString::dec_bufsize<T>()];
  62     auto int_to_str = IntegerToString::dec(val, buffer);
  63     if (int_to_str)
  64       return operator<<(*int_to_str);
  65     return *this;
  66   }
  67
  68   template <typename T, enable_if_t<is_floating_point_v<T>, int> = 0>
  69   StringStream &operator<<(T) {
  70     // If this specialization gets activated, then the static_assert will
  71     // trigger a compile error about missing floating point number support.
  72     static_assert(!is_floating_point_v<T>,
  73                   "Writing floating point numbers is not yet supported");
  74     return *this;
  75   }
  76
  77   // Write a null-terminated string. The terminating null character is not
  78   // written to allow stremaing to continue.
  79   StringStream &operator<<(const char *str) {
  80     return operator<<(string_view(str));
  81   }
  82
  83   // Write a single character.
  84   StringStream &operator<<(char a) {
  85     write(&a, 1);
  86     return *this;
  87   }
  88
  89   // Return true if any write operation(s) failed due to insufficient size.
  90   bool overflow() const { return err; }
  91
  92   size_t bufsize() const { return data.size(); }
  93 };
  94
  95 } // namespace cpp
  96 } // namespace __llvm_libc
  97
  98 #endif // LLVM_LIBC_SRC_SUPPORT_CPP_STRINGSTREAM_H