英文:
C++ Trying to write a method that changes a value in an extern vector
问题
以下是您要翻译的代码部分：
我有三个重要的文件：
main.cpp、common.h 和 EngineScript.cpp。我在 common 中声明了我的多维向量如下：
extern vector<vector<string>> PositionVector(vector<string>);
在 main.cpp 中定义它：
vector<vector<string>> PositionVector(20, vector<string>(20, " ")); // 用字符串填充向量，本例中为一个空格
在 EngineScript.cpp 中，我的方法如下：
class EngineObject : public EngineFunct {
public:
int objectXcord = 0;
int objectYcord = 0;
string objectIcon = "?";
void spawnObject() {
PositionVector[objectXcord][objectYcord] = objectIcon;
}
};
这段代码似乎存在一些问题，包括警告和错误。如果删除 spawnObject() 中的内容并将 PositionVector[obj.objectXcord][obj.objectYcord] = obj.objectIcon; 放入 main.cpp，它可以工作，但您想要的效果却无法实现。这个问题可能与指针和数组访问有关，但需要更多上下文信息才能确定问题的确切原因。希望这些信息对您有所帮助。
英文:
so I have three files here that are important:
main.cpp, common.h, EngineScript.cpp. I am declaring my multidimensional vector in common as extern vector<vector<string>> PositionVector(vector<string>);
I am defining it in main.cpp with
vector<vector<string>> PositionVector(20,vector<string>(20," ")); //populates the vector with a string, in this case, a space
my method looks like this in EngineScript.cpp
class EngineObject : public EngineFunct{
public:
int objectXcord = 0;
int objectYcord = 0;
string objectIcon = "?";
void spawnObject(){
PositionVector[objectXcord][objectYcord] = objectIcon;
}
};
this does not work.
it throws these errors
In file included from /home/jake/vstests/C++/ncurses_projects/ncurses_2dengineproject/main.cpp:17:
/home/jake/vstests/C++/ncurses_projects/ncurses_2dengineproject/EngineScript.cpp: In member function ‘void EngineObject::spawnObject()’:
/home/jake/vstests/C++/ncurses_projects/ncurses_2dengineproject/EngineScript.cpp:50:31: warning: pointer to a function used in arithmetic [-Wpointer-arith]
50 | PositionVector[objectXcord][objectYcord] = objectIcon;
| ^
/home/jake/vstests/C++/ncurses_projects/ncurses_2dengineproject/EngineScript.cpp:50:44: warning: pointer to a function used in arithmetic [-Wpointer-arith]
50 | PositionVector[objectXcord][objectYcord] = objectIcon;
| ^
/home/jake/vstests/C++/ncurses_projects/ncurses_2dengineproject/EngineScript.cpp:50:46: error: assignment of read-only location ‘*(PositionVector + (((sizetype)((EngineObject*)this)->EngineObject::objectXcord) + ((sizetype)((EngineObject*)this)->EngineObject::objectYcord)))’
50 | PositionVector[objectXcord][objectYcord] = objectIcon;
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~
make[2]: *** [CMakeFiles/Engine.dir/build.make:76: CMakeFiles/Engine.dir/main.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:83: CMakeFiles/Engine.dir/all] Error 2
make: *** [Makefile:91: all] Error 2>
whats really grinding my gears right now is that if i get rid of the contents of spawnObject()
and put PositionVector[obj.objectXcord][obj.objectYcord] = obj.objectIcon; into main.cpp, it does work, it works fine with no errors or bugs and does almost what I wanted. Its late, I am not that great at C++ and I can't seem to find anything helpful on the interwebs. what simple mistake am I making? thanks in advance
edit 1
after making the changes recommended by john, it gets farther along but still gives errors, just these ones look more annoying
[ 25%] Building CXX object CMakeFiles/Engine.dir/main.cpp.o
[ 50%] Building CXX object CMakeFiles/Engine.dir/EngineScript.cpp.o
[ 75%] Linking CXX executable Engine
/usr/bin/ld: CMakeFiles/Engine.dir/main.cpp.o: warning: relocation against `_Z14PositionVectorB5cxx11' in read-only section `.text._ZN12EngineObject11spawnObjectEv[_ZN12EngineObject11spawnObjectEv]'
/usr/bin/ld: CMakeFiles/Engine.dir/main.cpp.o: in function `EngineObject::spawnObject()':
main.cpp:(.text._ZN12EngineObject11spawnObjectEv[_ZN12EngineObject11spawnObjectEv]+0x23): undefined reference to `PositionVector[abi:cxx11]'
/usr/bin/ld: warning: creating DT_TEXTREL in a PIE
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/Engine.dir/build.make:129: Engine] Error 1
make[1]: *** [CMakeFiles/Makefile2:83: CMakeFiles/Engine.dir/all] Error 2
make: *** [Makefile:91: all] Error 2```
</details>
# 答案1
**得分**: 1
在common.h中：
```cpp
extern vector<vector<string>> PositionVector(vector<string>);
应该修改为：
extern vector<vector<string>> PositionVector;
你的版本声明了一个名为 PositionVector 的函数，这会让编译器感到困惑。
根据你得到的错误信息，似乎你没有在main.cpp中包含common.h。如果是这样的话，那么这是一个错误。你应该始终在声明全局变量的头文件中包含对应的全局定义的cpp文件。这可以让编译器有机会检查全局声明和全局定义是否一致。在上面的代码中，这是不成立的。
英文:
In common.h
extern vector<vector<string>> PositionVector(vector<string>);
should be
extern vector<vector<string>> PositionVector;
Your version declares a function called PositionVector which is confusing the compiler.
Judging by the errors you get it seems that you are not including common.h in main.cpp. If so then this is a mistake. You should always include the header file that makes a global declaration in the cpp file that makes the corresponding global definition. This gives the compiler a chance to check that the global declaration and global definition are consistent. Something that is not true in the code above.
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