功能与istream&参数C ++ [英] function with an istream& parameter C++

问题描述

我希望我的程序使用下面的函数readFile来读取文件。我试图找出如何用istream& amp; amp;参数。该函数的目标是通过接收文件名作为参数来读取文件。

  #include  
 #include< sstream> 
 #include< fstream> 
 #include< string> 
使用namespace std; 
 
 bool readFile（std :: istream& fileName）; //错误1 this line 
 
 int main（void）
 {
 string fileName; 
 
 cout<< 输入文件名称：; 
 cin>>文件名; 
 
 readFile（fileName）; // error 2 this line 
 
 
} 
 
 bool readFile（std :: istream& fileName）
 {
 ifstream file（fileName ，ios :: in）; //错误3这行
返回true; 
} 
  

我得到的三个错误：

错误1：在传递'bool readFile（std :: istream&）的参数1中'

错误2：无效的类型为'std： ：istream的&安培; {std :: basic_string}类型的表达式{aka std :: basic_istream&}'

错误3：无效的用户定义的从' std :: istream {aka std :: basic_istream}'到'const char *'[-fpermissive]

有反正我可以修复它吗？该函数的参数实际上必须保持std :: istream& fileName。

感谢您的帮助。

std :: ifstream 构造函数的第一个参数应该是一个字符串。您正在尝试将它传递给 std :: istream 。也许 std :: istream 包含你想要读取的文件的名字，在这种情况下，你想把名字提取到 std ::字符串首先。像这样的东西可能会工作：

  std :: string fileName; 
名称>>文件名; 
 std :: ifstream文件（fileName，ios :: in）; 
  

I would like my program to read a file using the function "readFile" below. I am trying to find out how to call a function with an istream& parameter. The goal of the function is to read the file by receiving the file's name as parameter.

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

bool readFile(std::istream& fileName); //error 1 this line

int main(void)
{   
    string fileName;

    cout << "Enter the file name: ";
    cin >> fileName;

    readFile(fileName); //error 2 this line


}

bool readFile(std::istream& fileName)
{
    ifstream file(fileName, ios::in); //error 3 this line
    return true;
}

The three errors I get:

error 1 : in passing argument 1 of 'bool readFile(std::istream&)

error 2 : invalid initialization of reference of type 'std::istream& {aka std::basic_istream&}' from expression of type 'std::string {aka std::basic_string}

error 3 : invalid user-defined conversion from 'std::istream {aka std::basic_istream}' to 'const char*' [-fpermissive]

Is there anyway I can fix it? The parameter of the function really has to remain "std::istream& fileName".

Thanks for helping.

解决方案

The first argument to the std::ifstream constructor should be a string. You're trying to pass it a std::istream. Maybe the std::istream contains the name of the file you want to read, in which case you want to extract the name into a std::string first. Something like this might work:

std::string fileName;
name >> fileName;
std::ifstream file(fileName, ios::in);

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