Question

我不熟悉静态类，并且从我的阅读中相信我已正确设置它，尽管我得到了一长串未定义的引用。如果有人可以告诉我正确的方法或我做错了会非常感激！

头文件：

 #ifndef _SYSTEMLOGGING_h
 #define _SYSTEMLOGGING_h
 #define BUF_LENGTH 45

 #if defined(ARDUINO) && ARDUINO >= 100
#include "Arduino.h"
 #else
#include "WProgram.h"
 #endif
 #include "EepromStorage.h"

 class SystemLogging
 {
 public:
    static bool writeLog(char logName[5], char timeStamp[9], char itemId[3], char deviceName[11], char value[6], char duration[5], char state[3] );

  private:
    static char logBuff[BUF_LENGTH];
    static char logname[9];
    static uint32_t length;
    static int lineCount;
    static int data;
 };


 #endif

c ++文件

 #include <SdFat.h>
 #include <SdFatUtil.h>
 #include "SystemLogging.h"

 extern SdFile g_file;
 extern SdFile g_root;


 bool SystemLogging::writeLog(char logName[5], char timeStamp[9], char itemId[3], char deviceName[11], char value[6], char duration[5], char state[3] ){
    memset(SystemLogging::logBuff, 0, BUF_LENGTH);
    strncpy (SystemLogging::logname, "XXXX.LOG", 9);
    strncpy (SystemLogging::logname, logName, 4);
    if (!g_file.open(&g_root,SystemLogging::logname, O_RDWR | O_CREAT )) { //create if dosent exist
        PgmPrintln("Log Write Error");
        return false;
    } else {
        SystemLogging::length = g_file.fileSize();
        g_file.setpos(0);
        SystemLogging::lineCount = 0;
        SystemLogging::data = 0;
        while((data = g_file.read()) > 0)
        {
            if(data == '\n')
                SystemLogging::lineCount++;
        }
        if(lineCount>99)
            g_file.setpos(0);
        strcpy(SystemLogging::logBuff,timeStamp + ':');
        strcat(SystemLogging::logBuff,itemId + ':');
        strcat(SystemLogging::logBuff,deviceName + ':');
        strcat(SystemLogging::logBuff,value + ':');
        strcat(SystemLogging::logBuff,duration + ':');
        strcat(SystemLogging::logBuff,state + '\n');
        g_file.print(SystemLogging::logBuff);
        g_file.close();
    }
    return false;
 }

编译错误：

 Compiling 'asas' for 'Arduino Mega 2560 or Mega ADK'
 SystemLogging.cpp.o : : In function `SystemLogging::writeLog(char*, char*, char*, char*, char*, char*, char*)':
 SystemLogging.cpp : logBuff'
 SystemLogging.cpp : logBuff'
 SystemLogging.cpp : logname'
 SystemLogging.cpp : logname'
 SystemLogging.cpp : logname'
 SystemLogging.cpp : logname'
 SystemLogging.cpp : logname'
 SystemLogging.cpp.o : :C:\Users\Tim\AppData\Local\VMicro\Arduino\Builds\asas\mega2560\SystemLogging.cpp:16: more undefined references to `SystemLogging::logname' follow
 SystemLogging.cpp.o : : In function `SystemLogging::writeLog(char*, char*, char*, char*, char*, char*, char*)':
 SystemLogging.cpp : length'
 SystemLogging.cpp : length'
 SystemLogging.cpp : length'
 SystemLogging.cpp : length'
 SystemLogging.cpp : lineCount'
 SystemLogging.cpp : lineCount'
 SystemLogging.cpp : data'
 SystemLogging.cpp : data'
 SystemLogging.cpp : lineCount'
 SystemLogging.cpp : lineCount'
 SystemLogging.cpp : lineCount'
 SystemLogging.cpp : lineCount'
 SystemLogging.cpp : data'
 SystemLogging.cpp : data'
 SystemLogging.cpp : lineCount'
 SystemLogging.cpp : lineCount'
 SystemLogging.cpp : logBuff'
 SystemLogging.cpp : logBuff'
 SystemLogging.cpp : logBuff'
 SystemLogging.cpp : logBuff'
 SystemLogging.cpp : logBuff'
 SystemLogging.cpp.o : :C:\Users\Tim\AppData\Local\VMicro\Arduino\Builds\asas\mega2560\SystemLogging.cpp:33: more undefined references to `SystemLogging::logBuff' follow
 Error creating .elf

感谢您的帮助！

Answer 1

类中static成员的声明只是声明，而不是定义。如果您实际使用任何static成员，则还需要定义它们。看来你没有提供定义：

// in your .cpp file add:
char     SystemLogging::logBuff[BUF_LENGTH];
char     SystemLogging::logname[9];
uint32_t SystemLogging::length;
int      SystemLogging::lineCount;
int      SystemLogging::data;

您可能也应该初始化变量，因为它们获得的值可能不是您想要的值。

BTW，名称_SYSTEMLOGGING_h保留供编译器及其标准库使用：除非明确允许，否则不允许在任何上下文中使用任何以下划线开头后跟大写字符的名称被使用（例如，__FILE__）。

Answer 2

您只在头文件中声明了静态成员，您需要在.cpp文件中定义它们。

char SystemLogging::logBuff[BUF_LENGTH] = {};
char SystemLogging::logname[9] = {};
uint32_t SystemLogging::length = 0;
int SystemLogging::lineCount = 0;
int SystemLogging::data = 0;

实际上，SystemLogging只包含静态成员和成员函数，更好地使用命名空间。我会选择std::string而不是char array。

带有私有静态成员的C ++“undefined references”

2 个答案: