AceUtils  0.1
Small and light Arduino utilties and libraries.
PrintString.h
1 /*
2 MIT License
3 
4 Copyright (c) 2020 Brian T. Park
5 
6 Permission is hereby granted, free of charge, to any person obtaining a copy
7 of this software and associated documentation files (the "Software"), to deal
8 in the Software without restriction, including without limitation the rights
9 to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
10 copies of the Software, and to permit persons to whom the Software is
11 furnished to do so, subject to the following conditions:
12 
13 The above copyright notice and this permission notice shall be included in all
14 copies or substantial portions of the Software.
15 
16 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
19 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
21 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
22 SOFTWARE.
23 */
24 
25 #ifndef PRINT_STRING_PRINT_STRING_H
26 #define PRINT_STRING_PRINT_STRING_H
27 
28 #include <stddef.h> // size_t
29 #include <Print.h>
30 
31 namespace print_string {
32 
63 class PrintStringBase: public Print {
64  public:
65  size_t write(uint8_t c) override {
66  if (index_ < size_ - 1) {
67  buf_[index_] = c;
68  index_++;
69  return 1;
70  } else {
71  return 0;
72  }
73  }
74 
75  size_t write(const uint8_t *buf, size_t size) override {
76  if (buf == nullptr) return 0;
77 
78  size_t n = 0;
79  while (size-- > 0) {
80  size_t ret = write(*buf++);
81  if (ret == 0) break;
82  n++;
83  }
84  return n;
85  }
86 
87 // ESP32 version of Print class does not define a virtual flush() method so
88 // we can't use the 'override' keyword.
89 #ifdef ESP32
90  void flush() {
91  index_ = 0;
92  }
93 #else
94  void flush() override {
95  index_ = 0;
96  }
97 #endif
98 
104  const char* getCstr() const {
105  buf_[index_] = '\0';
106  return buf_;
107  }
108 
110  size_t length() const {
111  return index_;
112  }
113 
114  protected:
115  PrintStringBase(uint16_t size, char* buf):
116  size_(size),
117  buf_(buf) {}
118 
119  private:
120  uint16_t const size_;
121  uint16_t index_ = 0;
122 
123  // This is the pointer to actualBuf_ which is defined in the subclasses.
124  // Instead of storing it (and taking up precious RAM), maybe there's a way
125  // to calculate this pointer by simply extending the pointer from the last
126  // element of this object (i.e. &index_), and thereby saving some memory.
127  // But I am not convinced that I have the knowledge do that properly
128  // without triggering UB (undefined behavior) in the C++ language. Do I
129  // define buf_[0] here and will it point exactly where actualBuf_[] is
130  // allocated? Or do I use [&PrintStringBase + sizeof(PrintStringBase)] to
131  // calculate the pointer to actualBuf_. I just don't know what's actually
132  // allowed in the language spec versus something that works by pure luck on
133  // a particular microcontroller and compiler. So I'll pay the cost of the 2
134  // extra bytes (8-bit) or 4 extra bytes (32-bit processors) of RAM and
135  // store the pointer to actualBuf_ explicitly here in the base class.
136  char* const buf_;
137 };
138 
203 template <uint16_t SIZE>
205  public:
206  PrintString(): PrintStringBase(SIZE, actualBuf_) {}
207 
208  private:
209  char actualBuf_[SIZE];
210 };
211 
212 }
213 
214 #endif
print_string::PrintStringBase
Base class for all template instances of the PrintString<SIZE> class.
Definition: PrintString.h:63
print_string::PrintStringBase::length
size_t length() const
Return the length of the internal c-string buffer.
Definition: PrintString.h:110
print_string::PrintString
An implementation of Print that writes to an in-memory buffer supporting strings less than 65535 in l...
Definition: PrintString.h:204
print_string::PrintStringBase::getCstr
const char * getCstr() const
Return the NUL terminated c-string buffer.
Definition: PrintString.h:104