Question

我刚开始学习c ++和makefile。现在我被卡住了。似乎有很多像这样的问题，但我无法弄清楚哪种答案适用于我的情况。这个答案可能很明显。我非常感谢一些关于在哪里寻找以及我正在做的事情的原因的错误信息！

这是我的错误：

Undefined symbols for architecture x86_64:
  "App::init(char const*, int, int, int, int, bool)", referenced from:
      _main in main.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [../out/MYAPP] Error 1

这是我的代码：

的main.cpp

#include "App.h"

// our App object
App* a_app = 0;

int main(int argc, char* argv[])
{
    a_app = new App();

    a_app->init("Hello World", 100, 100, 640, 480, true);

    //...etc more code
    return 0;
}

App.h

#ifndef __App__
#define __App__

#include <SDL2/SDL.h>

class App
{
public:

    App(){}
    ~App(){}

    bool init(const char* title, int xpos, int ypos, int width, int height, bool fullscreen);
    //..etc
private:

};

#endif /* defined(__App__) */

App.cpp

#include "App.h"
#include <iostream>

using namespace std;

bool App::init(const char* title, int xpos, int ypos, int width, int height, bool fullscreen)
{   
    // attempt to initialize SDL
    if(SDL_Init(SDL_INIT_EVERYTHING) == 0)
    {
        cout << "SDL init success \n";

        int flags = 0;
        if(fullscreen)
        {
            flags = SDL_WINDOW_FULLSCREEN;
        }

        // init the window
        m_pWindow = SDL_CreateWindow(title, xpos, ypos, width, height, flags);
            //...etc 

    }
    else
    {
        cout << "SDL init fail \n";
        return false; // SDL init fail
    }

    cout << "SDL init success \n";
    m_bRunning = true; // everything inited successfully, start the main loop

    return true;
}

最后我的 makefile

CXX = clang++
SDL = -framework SDL2 -framework SDL2_image
INCLUDES = -I ~/Library/Frameworks/SDL2.framework/Headers -I ~/Library/Frameworks/SDL2_image.framework/Headers
CXXFLAGS = -Wall -c -std=c++11 $(INCLUDES)
LDFLAGS = $(SDL) -F ~/Library/Frameworks/
SRC = src
BUILD = build
OUT = ../out
EXE = $(OUT)/MYAPP

OBJECTS = $(BUILD)/main.o $(BUILD)/App.o

all: $(EXE)

$(EXE): $(OBJECTS) | $(OUT)
    $(CXX) $(LDFLAGS) $< -o $@

$(BUILD)/%.o : $(SRC)/%.cpp | $(BUILD)
    $(CXX) $(CXXFLAGS) $< -o $@ 

$(BUILD):
    mkdir -p $(BUILD)

$(OUT):
    mkdir -p $(OUT)

clean:
    rm $(BUILD)/*.o && rm $(EXE)

Answer 1

您没有链接所有目标文件。

$(CXX) $(LDFLAGS) $< -o $@

应该是

$(CXX) $(LDFLAGS) $^ -o $@

因为$<伪变量只扩展为第一个依赖项，即main.o。这与链接器错误匹配。

事实上，单独进行此修改会导致错误消失在我的计算机上。

架构x86_64的未定义符号，链接器命令失败

1 个答案: