c++ - Xcode 链接器错误 : linker command failed with exit code 1 (use -v to see invocation)

Question

使用 C++ 和 Xcode 我总是遇到链接器命令失败的问题。我不知道这是什么意思。我正在创建一个包含 3 个文件的基本程序。一个 main.cpp 和一个带有标题的类文件。主文件是空的。这是其他两个的样子:

学生.hpp :

#include <stdio.h>
#include <iostream>
#include <fstream>
#include <string>
#include <cmath>
#include <sstream>

std::string line;
class Student{
public:
    std::string fullName;
    int projectGrade;
    int quizGrade;
    int midtermGrade;
    int finalGrade;
    int finish;
    int start = 14;

    std::string getStudentName();
    int getProjectGrade();
    int getQuizGrade();
    int getMidtermGrade();
    int getFinalGrade();
    double getOverallGrade();
    bool login(std::string username, std::string password);
    bool login(std::string username);
};

学生.cpp:

#include "student.hpp"

std::string Student::getStudentName(){
    finish = line.find("\t", start);
    fullName = line.substr(start, finish);
    return fullName;
}
int Student::getProjectGrade(){
    start = line.find("\t", start) + finish;
    finish = start + 2;
    std::stringstream stream(line.substr(start, 2));
    stream >> projectGrade;
    return projectGrade;
}
int Student::getQuizGrade(){
    start+=3;
    std::stringstream stream(line.substr(start, 2));
    stream >> quizGrade;
    return quizGrade;
}
int Student::getMidtermGrade(){
    start+=3;
    std::stringstream stream(line.substr(start, 2));
    stream >> midtermGrade;
    return midtermGrade;
}
int Student::getFinalGrade(){
    start+=3;
    std::stringstream stream(line.substr(start, 2));
    stream >> finalGrade;
    return finalGrade;
}
double Student::getOverallGrade(){
    return round((projectGrade + quizGrade + midtermGrade + finalGrade)/40)*10;
}
bool Student::login(std::string username, std::string password){
    std::ifstream studentFile;
    studentFile.open("/Users/griffin/desktop/Data Structures/Data Structures1/Data Structures1/Students.txt");
    if(studentFile.is_open()){
        while(getline (studentFile,line))
        {
            if ((username.length() == 7 && username.substr(0,4).compare("u000") == 0 && line.find(username) != std::string::npos) && (password.length() == 6 && password.substr(0,2).compare("pw") == 0 && line.find(password) != std::string::npos))
                return true;
        }
    }
    return false;
}
bool Student::login(std::string username){

    std::ifstream studentFile;
    studentFile.open("/Users/griffin/desktop/Data Structures/Data Structures1/Data Structures1/Students.txt");
    if(studentFile.is_open()){
        while(getline (studentFile,line))
        {
            if (username.length() == 7 && username.substr(0,4).compare("u000") == 0 && line.find(username) != std::string::npos)
                return true;
        }
    }
    return false;
}

主文件包括student.hpp。这是 Xcode 端的问题还是我的代码有错误？

main.cpp

#include "student.hpp"    
int main(int argc, const char * argv[]) {
    return 0;
}

Answer 1

您的问题是您多次声明了全局变量 line。

没有充分的理由在您的代码中使用全局变量，因此简单的解决方案是在两个登录方法中声明 line。

然而，为了将来引用，这里是您应该如何声明全局变量

How do I use extern to share variables between source files?