c++ - 编译麻烦 - c++ 新手

Question

我是 c++ 的新手，这个类将与 flex 扫描仪一起使用。我在这里保持简单只是为了让它编译但我收到以下消息(关于此消息的其他线程似乎都不适用于我的情况):

Undefined symbols for architecture x86_64: "Listing::lexicalError", referenced from: Listing::Listing() in listing.o Listing::displayErrorCount() in listing.o Listing::increaseLexicalError() in listing.o ld: symbol(s) not found for architecture x86_64

list .h

using namespace std;

class Listing
{

public:
  enum ErrorType {LEXICAL, SYNTAX, SEMANTIC};

Listing();

void appendError(ErrorType error, char yytext[]);

void displayErrorCount();

void increaseLexicalError();

private:

static int lexicalError;

};

list .cpp

#include <iostream>
#include <sstream>
using namespace std;

#include "Listing.h"


Listing::Listing()
{
  lexicalError = 0;
}

void Listing::appendError(ErrorType error, char yytext[])
{
    switch (error) {
        case LEXICAL:
            cout << "Lexical Error, Invalid Character " << yytext << endl;
            break;
        case SEMANTIC:
            cout << "Semantic Error, ";
        case SYNTAX:
            cout << "Syntax Error, ";

    default:
        break;
}
}

void Listing::displayErrorCount()
{
    cout << "Lexical Errors " << lexicalError << " ";

}

void Listing::increaseLexicalError()
{
  lexicalError++;
}

感谢您提供的编译帮助。我确定 C++ 代码不漂亮，但我正在学习 ...

这是生成文件:

compile: scanner.o listing.o
    g++ -o compile scanner.o listing.o

scanner.o: scanner.c listing.h tokens.h
    g++ -c scanner.c

scanner.c: scanner.l
    flex scanner.l
    mv lex.yy.c scanner.c

listing.o: listing.cpp listing.h
    g++ -c listing.cpp

Answer 1

您必须在 .cpp 文件中定义静态成员变量 lexicalError:

#include <iostream>
#include <sstream>
using namespace std;

#include "Listing.h"

// here is the definition
int Listing::lexicalError = 0;

Listing::Listing()
{
  // not sure if you really want to do this, it sets lexicalError to zero
  // every time a object of class Listing is constructed
  lexicalError = 0;
}

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