加速的C++：体系结构x86_64的未定义符号

Question

我正在通过加速C++，我无法从第4章获得程序编译;这是第一个标题。我也从here下载了源代码，并得到了与手抄代码完全相同的错误，所以我不确定问题所在。

我在OSX El Capitan上使用g ++。下面是我用的确切命令：

$ g++ main.cpp 

这里的错误：

Undefined symbols for architecture x86_64: 
    "read(std::__1::basic_istream<char, std::__1::char_traits<char> >&, Student_info&)", referenced from: 
     _main in grades-main-e0475a.o 
    "grade(Student_info const&)", referenced from: 
     _main in grades-main-e0475a.o 
    "compare(Student_info const&, Student_info const&)", referenced from: 
     _main in grades-main-e0475a.o 
ld: symbol(s) not found for architecture x86_64 
clang: error: linker command failed with exit code 1 (use -v to see invocation) 

而这里的代码：

的main.cpp

#include <algorithm> 
#include <iomanip> 
#include <ios> 
#include <iostream> 
#include <stdexcept> 
#include <string> 
#include <vector> 
#include "grade.h" 
#include "Student_info.h" 

using namespace std; 

int main() { 

    vector<Student_info> students; 
    Student_info record; 
    string::size_type maxlen = 0; // length of the longest name 

    while (read(cin, record)) { 
    maxlen = max(maxlen, record.name.size()); 
    students.push_back(record); 
    } 

    sort(students.begin(), students.end(), compare); 

    for (vector<Student_info>::size_type i = 0; i != students.size(); i++) { 
    cout << students[i].name << string(maxlen + 1 - students[i].name.size(), ' '); 

    try { 
     double final_grade = grade(students[i]); 
     streamsize prec = cout.precision(); 
     cout << setprecision(3) << final_grade << setprecision(prec); 
    } catch (domain_error e) { 
     cout << e.what(); 
    } 
    cout << endl; 
    } 

    return 0; // success 
} 

grade.h

#ifndef GUARD_grade_h 
#define GUARD_grade_h 

#include <vector> 
#include "Student_info.h" 

double grade(double, double, double); 
double grade(double, double, const std::vector<double>&); 
double grade(const Student_info&); 

#endif 

grade.cpp

#include <stdexcept> 
#include <vector> 
#include "grade.h" 
#include "median.h" 
#include "Student_info.h" 

using namespace std; 

double grade(double midterm, double final, double homework) { 
    return 0.2 * midterm + 0.4 * final + 0.4 * homework; 
} 

double grade(double midterm, double final, const vector<double>& hw) { 
    if (hw.size() == 0) throw doman_error("student has done no homework"); 

    return grade(midterm, final, median(hw)); 
} 

double grade(const Student_info& s) { 
    return grade(s.midterm, s.final, s.homework); 
} 

Student_info.h

#ifndef GUARD_Student_info 
#define GUARD_Student_info 

#include <iostream> 
#include <string> 
#include <vector> 

struct Student_info { 
    std::string name; 
    double midterm, final; 
    std::vector<double> homework; 
}; 

bool compare(const Student_info&, const Student_info&); 
std::istream& read(std::istream&, Student_info&); 
std::istream& read_hw(std::istream&, std::vector<double>&); 

#endif 

Student_info.cpp

#include "Student_info.h" 

using namespace std; 

bool compare(const Student_info& x, const Student_info& y) { 
    return x.name < y.name; 
} 

istream& read(istream& is, Student_info& s) { 
    is >> s.name >> s.midterm >> s.final; 

    read_hw(is, s.homework); 
    return is; 
} 

istream& read_hw(istream& in, vector<double>& hw) { 
    if (in) { 
    hw.clear(); 

    double x; 
    while (in >> x) { 
     hw.push_back(x); 
    } 
    in.clear(); 
    } 
    return in; 
} 

median.h

#ifndef GUARD_median_h 
#define GUARD_median_h 

#include <vector> 

double median(std::vector<double>); 

#endif 

median.cpp

#include <algorithm> 
#include <stdexcept> 
#include <vector> 

using namespace std; 

double median(vector<double> vec) { 
    typedef vector<double>::size_type vec_sz; 

    vec_sz size = vec.size(); 
    if (size == 0) throw domain_error("median of an empty vector"); 

    sort(vec.begin(), vec.end()); 

    vec_sz mid = size/2; 

    return size % 2 == 0 ? (vec[mid] + vec[mid-1])/2 : vec[mid]; 
} 

非常感谢您的帮助，任何人！

Answer 1

正如@ gudok的有点神秘的评论所暗示的，这很可能是您的第一个带有多个源文件的程序。你不能只编译一个文件并获得可执行文件;您必须编译每个文件并将生成的目标文件链接在一起。要做到这一点最简单的方法是这样的：

g++ main.cpp grade.cpp student_info.cpp median.cpp 

如果在代码中没有错误，将产生在当前目录下一个名为“a.out的”可执行文件。

编辑：只注意到该错误消息来自“铛”，而不是“G ++”这没关系;如果你使用。‘铛’，只是改变了命令行

clang++ main.cpp grade.cpp student_info.cpp median.cpp