构造函数在定义时使用自身时出错

Question

Error 1 error C2460: 'Square::string' : uses 'Square', which is being defined

Hello everyone, I am getting the following error while trying to implement my 4-square cipher. I have two constructors in the Square header and .cpp file. One of them takes no parameters while the other is taking a string. The one with the string is throwing the error.

square.h

#include <string>

#ifndef SQUARE_H
#define SQUARE_H
class Square
{
public:
    Square();
    Square(string);
    ~Square();
    char mat[5][5];
    bool used[25];
    char getChar(int, int);
    int* getPos(char);

};

#endif

Here is the layout of it in the .cpp file.

Square::Square(string s)
{
//Code in here can show on request!
}

I think the string piece has something to do with it but I am not sure.

Answer 1

Instead of

Square( string );

you need

Square( std::string );

There may be other errors in the code not shown.

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Not an error, but usually a std::string is passed by reference, to avoid needless copying.

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Also, tip: with modern compilers, instead of include guards you can just use #pragma once . Keeping in mind that it's a universally supported de facto standard, not part of the official standard. I find it cleaner, somehow, and it alleviates the need to come up with distinct, unique include guard symbols.

Answer 2

There's not enough to really know what's going on here. Everything looks fine from what you have.

Maybe you need the namespace?

Square(std::string);

Answer 3

See (here on so: Error : Class A uses Class B, which is being defined ) and also here .

string is the problem. It's from std namespace so prefix every occurrence of string with 'std::', eg for your header:

#include <string>

#ifndef SQUARE_H
#define SQUARE_H
class Square
{
public:
    Square();
    Square(std::string);
    ~Square();
    char mat[5][5];
    bool used[25];
    char getChar(int, int);
    int* getPos(char);

};