我试图在Arduino和面包板上创建一个伪媒体中心的东西，并不是那么复杂但是这是我的第一个C ++项目，其数量超过＆＃ 39; Hello world！＆＃39;或计算器。
尽管如此，我开始重写几乎整个原始程序，并努力清理，开始使用地图来保存键和值（IR代码），并进一步组织它，把函数内部的赋值（IR_generateMap（）），但我在编译时遇到错误。
C:\Users\trevo\Documents\Arduino\improvedIRRemote\improvedIRRemote.ino: In function 'void IRLoop(bool)':
improvedIRRemote:78: error: call to non-constexpr function 'std::map<Key, T, Compare, Allocator>::reference std::map<Key, T, Compare, Allocator>::operator[](const key_type&) [with Key = std::basic_string<char>; T = int; Compare = std::less<std::basic_string<char> >; Allocator = std::allocator<int>; std::map<Key, T, Compare, Allocator>::reference = int&; std::map<Key, T, Compare, Allocator>::key_type = std::basic_string<char>]'
case IRCodes["Power Button"]:
^
improvedIRRemote:78: error: call to non-constexpr function 'std::map<Key, T, Compare, Allocator>::reference std::map<Key, T, Compare, Allocator>::operator[](const key_type&) [with Key = std::basic_string<char>; T = int; Compare = std::less<std::basic_string<char> >; Allocator = std::allocator<int>; std::map<Key, T, Compare, Allocator>::reference = int&; std::map<Key, T, Compare, Allocator>::key_type = std::basic_string<char>]'
exit status 1
call to non-constexpr function 'std::map<Key, T, Compare, Allocator>::reference std::map<Key, T, Compare, Allocator>::operator[](const key_type&) [with Key = std::basic_string<char>; T = int; Compare = std::less<std::basic_string<char> >; Allocator = std::allocator<int>; std::map<Key, T, Compare, Allocator>::reference = int&; std::map<Key, T, Compare, Allocator>::key_type = std::basic_string<char>]'
我抬头试图理解非constexpr电话的错误，但说实话，我不明白我试图用地图做的事与我有什么关系。在处理上述错误的帖子中描述的问题。
#include <IRremote.h>
#include <StandardCplusplus.h>
#include <map>
//Variables responsible for recieving and decoding IR signals/codes.
IRrecv receiver(10); //IR receiver initialization.
decode_results results; //Object that is responsible for decoding the IR signal.
//Variables responsible for tracking channel changing.
int channel = 1; //The active channel.
int desiredChannel = ""; //The string that is used to concatenate the numbers pressed on the remote keypad together.
int channelEnterDelay = 4000; //The delay between the last time a number was pressed on the remote keypad and when the desiredChannel is cleared.
unsigned long channelEnterStartTime = 0; //The time in which that last number was pressed on the remote keypad.
String intConverter; //The string responsible for casting an integer to a string.
//Variables responsible for tracking volume changing.
int volume = 50; //The current volume.
int lastVolume = 50; //Holds the value of the volume previous to the volume being muted.
bool isMuted = false; //Whether or not the sound has been muted.
//Map responsible for the setting and getting of IR codes and their respective keys.
const std::map<std::string, int> IRCodes;
//Miscellanious Stuff - mostly waiting for depreciation.
int IRFlasherPin = 8;
int mode = 0;
int IRFlasherBlinkRate = 10;
//Debug mode shows channel switching info when entering from the remote keypad, turn it off to declutter the serial feed if it is not being used.
bool DEBUG_MODE = false;
void setup() {
receiver.enableIRIn(); //Tells the receiver to start listening for IR communication.
pinMode(IRFlasherPin, OUTPUT); //Configuring the pin that flashes upon recieving the 'excess communication' IR code.
Serial.begin(9600); //Begins serial communication at 9600 baud.
IR_generateMap(); //Sets all of the values for the map of IR keys and values.
//Ready message.
Serial.println("The Arduino is ON and ready for communication.");
if (DEBUG_MODE) { Serial.println("Also please note that debug mode has been preemptively enabled. The serial monitor can be expected to be much more cluttered than normal. To disable this, press the 'U/SD' button on the remote."); }
Serial.println();
}
void loop() {
//Pre-loop checks.
//empty
IRLoop(true);
}
void IRLoop(bool toldToContinueLooking) {
if (receiver.decode(&results)) {
switch(results.value) {
case IRCodes["Power Button"]:
Serial.println("Power Toggle");
break;
default:
if (DEBUG_MODE) {
Serial.print("Extraneous code: ");
Serial.print(results.value);
}
break;
}
}
if (toldToContinueLooking) { receiver.resume(); }
}
void IR_generateMap() {
//General Keys
IRCodes["Power Button"] = 16753245;
IRCodes["Mode Button"] = 16736925;
IRCodes["Back Button"] = 16750695;
IRCodes["EQ Button"] = 16769055;
IRCodes["USD Button"] = 16756815;
//Media Keys
IRCodes["PlayPause Button"] = 16720605;
IRCodes["Rewind Button"] = 16712445;
IRCodes["Fast Forward Button"] = 16761405;
//Volume Keys
IRCodes["Mute Button"] = 16769565;
IRCodes["Minus Button"] = 16754775;
IRCodes["Plus Button"] = 16748655;
//Numpad Keys
IRCodes["Numpad 0"] = 16738455;
IRCodes["Numpad 1"] = 16724175;
IRCodes["Numpad 2"] = 16718055;
IRCodes["Numpad 3"] = 16743045;
IRCodes["Numpad 4"] = 16716015;
IRCodes["Numpad 5"] = 16726215;
IRCodes["Numpad 6"] = 16734885;
IRCodes["Numpad 7"] = 16728765;
IRCodes["Numpad 8"] = 16730805;
IRCodes["Numpad 9"] = 16732845;
//Non-Key Codes
IRCodes["Excess Communication"] = 4294967295;
}
根据我早期C ++知识库中的某个人能够理解，有人可以向我解释我做错了什么吗？
答案 0 :(得分：0)
'case'中的表达式必须是编译时常量。只需使用if / else结构，它就可以工作。
托马斯
答案 1 :(得分：0)
我使用map解码IR Code处理函数或使用enum以相反的方式行事。像这样：
#include <StandardCplusplus.h>
#include <map>
#include <functional>
void power_key();
void num_key0();
void num_key1();
void num_key2();
void num_key3();
void num_key4();
void num_key5();
void num_key6();
void num_key7();
void num_key8();
void num_key9();
void num_key(int8_t);
typedef void(*handler_t)();
std::map<uint32_t, handler_t> keys;
void setup() {
keys[16753245UL] = power_key;
keys[16738455UL] = num_key0;
keys[16724175UL] = num_key1;
keys[16718055UL] = num_key2;
keys[16743045UL] = num_key3;
keys[16716015UL] = num_key4;
keys[16726215UL] = num_key5;
keys[16734885UL] = num_key6;
keys[16728765UL] = num_key7;
keys[16730805UL] = num_key8;
keys[16732845UL] = num_key9;
Serial.begin(57600);
}
void loop() {
uint32_t recvd_code = 16753245UL; // literal value, for testing purpose without IR receiver and remote
auto iter = keys.find(recvd_code); // find received code and execute it
if (iter != keys.end()) {
iter->second();
} else {
Serial.print(F("IR Code "));
Serial.print(recvd_code);
Serial.println(F("not found"));
}
delay(1000);
}
void power_key() {
Serial.println(F("Power key pressed"));
}
void num_key0() { num_key(0); }
void num_key1() { num_key(1); }
void num_key2() { num_key(2); }
void num_key3() { num_key(3); }
void num_key4() { num_key(4); }
void num_key5() { num_key(5); }
void num_key6() { num_key(6); }
void num_key7() { num_key(7); }
void num_key8() { num_key(8); }
void num_key9() { num_key(9); }
void num_key(int8_t num) {
Serial.print(F("Numeric key pressed: "));
Serial.println(num);
}
初始化程序列表在某种程度上起作用，因此必须在设置中进行初始化，而map不能const。