错误:‘::main’必须返回‘int’ [英] error: ‘::main’ must return ‘int’

问题描述

我目前在课堂上使用 Putty 虚拟机 (UNIX)，我们正在做一个简短的 C++ 作业.任务是:创建一个 C++ 程序来测试文件帐户是否存在并打印一条消息来说明文件是否存在"

这就是我所拥有的，但是当我尝试编译代码时，出现此错误:错误:‘::main’必须返回‘int’

#include#include使用命名空间标准；内联 bool exists_test1 (const std::string& name) {if (FILE *file = fopen(name.c_str(), "r")) {fclose(文件)；返回真；} 别的 {返回假；}}无效主(){字符串 s;cout<<"输入文件名";cin>s;bool ans =exists_test1(s);如果(答案){cout<<文件存在"<<endl;}别的{cout<<"文件不存在";}}

解决方案

main 的返回类型为 int.这是由 C++ 标准定义的.在我的 C++11 草案的本地副本中，它在 § 3.6.1 Main Function 中进行了概述:

<块引用>

2. 一个实现不应预定义主函数.该函数不得重载.它应该有一个int类型的返回类型，否则它的类型是实现定义的.所有实现都应该允许main的以下两个定义:

   int main() {/* ... */}

   和

   int main(int argc, char* argv[]) {/* ... */}

因此，根据标准，您的程序格式不正确，您的编译器正确地将其报告为错误.将您的函数定义为:

int main(){//你的代码...返回0；}

I am currently using Putty virtual machine (UNIX) for my class, and we are doing a short C++ assignment. The assignment is to: "Create a C++ program that tests to see if the file accounts exists and prints a message to say whether the file exists"

This is what I have, but when I try to compile the code, I get this error: error: ‘::main’ must return ‘int’

#include<iostream>
#include<fstream>

using namespace std;
inline bool exists_test1 (const std::string& name) {

if (FILE *file = fopen(name.c_str(), "r")) {
fclose(file);
return true;
} else {
return false;
}
}

void main()
{
string s;
cout<<"Enter filename";
cin>>s;
bool ans =exists_test1(s);
if(ans)
{
cout<<"File Exist"<<endl;
}
else
{
cout<<"File Does not Exist";
}
}

解决方案

The return type of main is int. This is defined by the C++ standard. In my local copy of the C++11 draft it's outlined in § 3.6.1 Main Function :

2. An implementation shall not predefine the main function. This function shall not be overloaded. It shall have a return type of type int, but otherwise its type is implementation-defined. All implementations shall allow both of the following definitions of main:

   int main() { /* ...  */ }
   

   and

   int main(int argc, char* argv[]) { /* ...  */ }
   

Therefore your program is ill-formed according to the standard, and you compiler is rightly reporting it as an error. Define your function instead as:

int main()
{
    // your code...

    return 0;
}

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