声明函数指针 C++ arduino 1.6.11

Question

我是 C++ 的初学者，但对于我的 arduino，我需要这段代码。它正在为较低版本的 arduino 编译和工作，例如arduino-1.6.5.r5。从 1.6.9 开始，甚至是最新版本的 arduino (1.6.11)，此声明不再编译。我完全不明白这个错误。可以用另一种方式重写吗？我正在使用图书馆 CallBack.h.

图书馆来源： https://bitbucket.org/ehsmaes/cmdcallback/wiki/Home

图书馆的例子 `

#include <CallBack.h>
// Compile and upload to arduino. Run the serial monitor and type command
// :help;
// Values for initiation of cmd/response interface. 
// After initial boot, id, gid and del are stored in eeprom.
// Change values by command. Make sure each device has a unique id.
String descr="Command/response test program v0.1";
String id="a1";
String gid="a";
int    del=0; //delayed response

// List of commands defined by keyword, funtion pointer, number of arguments 
// and description used in "help" command.
CallBackDef f[] = {
  {(String)"add",   (FunctionPointer)&add,  (int)2, (String)":num1:num2"}
};

// initiate command handler: function array, number of functions and intial values
CallBack cmd(f, sizeof(f) / sizeof(*f), id, gid, descr, del);

void setup() {
  Serial.begin(9600);
  cmd.ok(); // say hello
}

void loop() {
  // Put code here. Use timers instead of delay if possible as not to disrupt
  // command/response interaction with host
}

void serialEvent() {
  // Don't forget this line. Parse command if serial data is available.
  cmd.cmdCheck();
}

//   --------- command initiated callback functions below ---------
// callback functions all need to be defined void and with String argv
// argument list. The command parser will validate the number of input
// parameters but any additional validation has to be perfomed by each
// callback function. As the argument list is passed as strings, type
// casting to other types is the responsibility of the function.


void add(String argv[]) {
  int a = cmd.stoi(argv[0]);
  int b = cmd.stoi(argv[1]);
  cmd.respond(String(a + b));
}

`

    CmdCallBack_example_minimum:17: error: 'add' was not declared in this scope
   {(String)"add",   (FunctionPointer)&add,  (int)2, (String)":num1:num2"}
                                       ^
Using library CmdCallBack in folder: /Users/adrian/ownCloud/Arduino/libraries/CmdCallBack (legacy)
exit status 1
'add' was not declared in this scope

Answer 1

此错误意味着函数 baseevent 未在 CallBackDef f[] = ... 之前声明。您在使用前需要函数原型，或函数定义（= 在使用前完成函数）。

Arduino 中还有另一个预处理器，负责处理这些定义并将它们放在草图开始附近的某个位置。但是任何更复杂的东西通常都会被破坏（生成的原型是完全错误的），所以即使是合法的 c++ 代码也无法编译。它有时会改变它在 Arduino 版本之间的行为。

示例 CmdCallBack_example_minimum 在 1.6.9 中默认不工作，但是，如果您添加函数原型：

#include <CallBack.h>

// Compile and upload to arduino. Run the serial monitor and type command
// :help;

// Values for initiation of cmd/response interface. 
// After initial boot, id, gid and del are stored in eeprom.
// Change values by command. Make sure each device has a unique id.
String descr="Command/response test program v0.1";
String id="a1";
String gid="a";
int    del=0; //delayed response
byte   echo=1; // command back to host

// ------------------------------------------------
// Function Prototype for add:
void add(String argv[]);

// List of commands defined by keyword, funtion pointer, number of arguments 
// and description used in "help" command.
CallBackDef f[] = {
  {(String)"add",   (FunctionPointer)&add,  (int)2, (String)":num1:num2"}
};

// initiate command handler: function array, number of functions and intial values
CallBack cmd(f, sizeof(f) / sizeof(*f), id, gid, descr, del, echo);

void setup() {
  Serial.begin(9600);
  cmd.ok(); // say hello
}

void loop() {
  // Don't forget this line. Parse command if serial data is available.
  cmd.cmdCheck();

  // Put code here. Use timers instead of delay if possible as not to disrupt
  // command/response interaction with host


}

//   --------- command initiated callback functions below ---------
// callback functions all need to be defined void and with String argv
// argument list. The command parser will validate the number of input
// parameters but any additional validation has to be perfomed by each
// callback function. As the argument list is passed as strings, type
// casting to other types is the responsibility of the function.

void add(String argv[]) {
  int a = cmd.stoi(argv[0]);
  int b = cmd.stoi(argv[1]);
  cmd.respond(String(a + b));
}

没有显式函数原型，Arduino 预处理器会处理它，但它会插入到使用它的行之后。所以还是有错误。

然而，即使在该修复之后，您的版本也已损坏（CallBack cmd 中的一些不正确的参数类型...）

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