c++ - C++ 未定义对 main 的引用时出错

Question

我一直收到错误提示...

(.text+0x20): undefined reference to `main'
collect2: ld returned 1 exit status
make: *** [FuelGauge] Error 1

下面是我的项目以及我的代码和 makefile。此外，如果您发现任何其他编码错误，请随时指出它们 =]

模拟器类

 #include <iostream>
 #include <iomanip>
 #include "FuelGauge.h"
 #include "Odometer.h"

 using namespace std;

 int main(){
    FuelGauge fuel(0); return 0; 
 }

FuelGauge 类

#include "FuelGauge.h"
#include <iostream>
#include <cstdlib>

using namespace std;
void FuelGauge::incrementGas(int gas){
    if(currentFuel < maxGallon) {
        currentFuel++;
    }
}
int FuelGauge::getGas(){
    return currentFuel;
}

FuelGauge.h

class FuelGauge {

private: 
            int currentFuel;
            int maxGallon;

public:
            void incrementGas(int);
            int getGas();           
};

里程表类

#include "FuelGauge.h"
#include "Odometer.h"
#include <iostream>
#include <cstdlib>
using namespace std;

private: int currentMileage;
Odometer::Odometer(){
    mileage = 0;
    Fuelgauge g;
}

int Odometer::getMileage(){
    return mileage;
}

void Odometer::incrementMileage(){
    if(mileage <= 999999){
    mileage++;
}
else{
    mileage = 0;
}

void Odometer::decreaseMileage(){

    if(g.currentFuel > 24){
        g.currentFuel--;
    }
 }
}

里程计.h

class Odometer{

private:
    int mileage;
    int gallons;
}

生成文件

FLAGS = -Wall
CC = g++
SYMBOLS = -g

all: FuelGauge Odometer CarSimulatorDemo

FuelGauge: FuelGauge.cpp FuelGauge.h
    $(CC) $(FLAGS) $(SYMBOLS) -o $@ FuelGauge.cpp
Odometer: Odometer.cpp Odometer.h
    $(CC) $(FLAGS) $(SYMBOLS) -o $@ Odometer.cpp    
CarSimulatorDemo: CarSimulatorDemo.cpp
    $(CC) $(FLAGS) $(SYMBOLS) -o $@ CarSimulatorDemocpp
clean:
    rm FuelGauge Odometer CarSimulatorDemo

Answer 1

您遇到的问题可能不是因为您的 C++ 代码，而是因为您的 Makefile。您希望将每个 cpp 文件编译为目标文件而不是单独的应用程序，然后将它们链接在一起成为单个应用程序。要将 cpp 编译为 .o 文件，请使用 -c 选项。

总结一下你的 Makefile 应该如下:

FLAGS = -Wall
CC = g++
SYMBOLS = -g

all: app

app: FuelGauge.o Odometer.o CarSimulatorDemo.o
    $(CC) $(FLAGS) $(SYMBOLS) *.o -o app
FuelGauge.o: FuelGauge.cpp FuelGauge.h
    $(CC) $(FLAGS) $(SYMBOLS) -c -o FuelGauge.o FuelGauge.cpp
Odometer.o: Odometer.cpp Odometer.h
    $(CC) $(FLAGS) $(SYMBOLS) -c -o Odometer.o Odometer.cpp    
CarSimulatorDemo.o: CarSimulatorDemo.cpp
    $(CC) $(FLAGS) $(SYMBOLS) -c -o CarSimulatorDemo.o CarSimulatorDemo.cpp
clean:
    rm FuelGauge.o Odometer.o CarSimulatorDemo.o app

记住将 Makefile 中的空格更改为制表符!

附言。 #ifndef 应始终暗示使用 #endif 并且在头文件中始终使用它们!