如何通过函数参数使用fstream（特别是ofstream） [英] How do I use fstream (specifically ofstream) through a functions parameters

问题描述

您好，我是一个 c ++ 初学者，这是我的任务之一，我有点卡住。这不是我的整个代码它只是一个我需要帮助的片段。我想做的是有一个函数专门用于导出一切与该函数到一个文本文件，称为results.txt。因此，当我打开文件时，应该出现这个工作行，但当我运行该文件，我得到错误像

Hi I'm a c++ beginner and this is one of my assignments and I'm a bit stuck. This isn't my entire code it's just a snippet of what I need help with. What I'm trying to do is have one function dedicated to exporting everything with that function into a text file which is called results.txt. So the line "does this work" should show up when I open the file, but when I run the file I get errors like

错误C2065：'out'：未声明的标识符

"Error C2065: 'out' : undeclared identifier"

错误C2275：'std :: ofstream'：非法使用此类型作为表达式

"Error C2275: 'std::ofstream' : illegal use of this type as an expression"

IntelliSense：类型名称不允许

"IntelliSense: type name is not allowed"

IntelliSense：标识符未定义

"IntelliSense: identifier "out" is undefined"

#include <iostream>
#include <string>
#include <fstream>


using namespace std;

//prototypes
void output(ofstream& out);

int main()
{
output(ofstream& out);
    ifstream in;
    in.open("inven.txt");
    ofstream out;
    out.open("results.txt");
return 0;
}

void output(ofstream& out)
{
out << "does this work?" << endl;
}

现在真的很晚了，

推荐答案

首先，这是很好的：

void output(ofstream& out)
{
    out << "does this work?" << endl;
}

但是，这不是：

int main()
{
    output(ofstream& out); // what is out?
    ifstream in;
    in.open("inven.txt");
    ofstream out;
    out.open("results.txt");
return 0;
}

这是您遇到的第一个错误：错误C2065：'out'：未声明的标识符，因为编译器不知道。

This is the first error you get: "Error C2065: 'out' : undeclared identifier", because the compiler doesn't know about out yet.

在第二个片段中， code> ostream& 。不是调用函数，而是给出一个函数声明，在本上下文中不允许。你必须使用给定的 ostream& 来调用它：

In the second fragment you want to call output with a specific ostream&. Instead of calling a function, you're giving a function declaration, which isn't allowed in this context. You have to call it with the given ostream&:

int main()
{
    ifstream in;
    in.open("inven.txt");
    ofstream out;
    out.open("results.txt");
    output(out); // note the missing ostream&
    return 0;
}

在这种情况下，您可以 输出与 out 作为参数。

In this case you call output with out as parameter.

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