如何从 c++ 中的文件读入 [暂停]

Question

I am having trouble reading in characters from a file. When this code runs it says it cannot read in from the file. The text file is in the same folder as main.cpp (not sure if this is a problem).

char read_from_file;

std::cout << "You picked a pre-written file to play against" << std::endl;
std::cout << "A pre determined choice has been picked, what do you choose?" << std::endl;

std::ifstream inFile;
inFile.open("rps.txt");
inFile >> read_from_file;

if (inFile.is_open())
{
   std::cout << "Successful" << std::endl;
}
else
{
   std::cout << "Unable to open file" << std::endl;
}
inFile.close();

Answer 1

Try full path to "rps.txt". It should work.

Answer 2

It sounds like you've got this already, but just for completeness, the file you want to read from should be in the same directory as your executable.

dir
  |- main.cpp
  |- rps.txt
  |- a.out*

* or whatever the name of your program is

I just put a single 'R' in my rps.txt file. Your code is mostly good. There is one key difference, and that is that you need to check that you opened the file immediately after you attempt to open it. You need to know if it's open before you try to read from it.

#include <iostream>
#include <fstream>

int main()
{
    char read_from_file;

    std::cout << "You picked a pre-written file to play against" << std::endl;
    std::cout << "A pre determined choice has been picked, what do you choose?" << std::endl;

    std::ifstream inFile;
    inFile.open("rps.txt");
    if (!inFile.is_open())  // You would probably flesh this out with an error
        return 1;           // message or something

    inFile >> read_from_file;

    if (inFile.is_open())
        std::cout << "Successful" << std::endl;
    else
        std::cout << "Unable to open file" << std::endl;
    inFile.close();
}

This worked just fine for me. You are not specific on what your error message is. Are you getting the "Unable to open file" from your code, or are you getting a system message? The solution is likely to ensure that the file can be read from, and maybe also executed. For safety, you can run chmod 777 rps.txt * from a terminal to give full permissions to the file.

I'm also going to comment that because all of my if and else statements are just single statements, I am safe to leave out the { } . If you need a block to more than one thing, bring back the curly braces, and if one branch of a larger block requires curly braces, then all branches should get them for consistency/readability.

* Linux and macOS. You can right click a file in Windows and set permissions there. Probably PowerShell too, but I don't have the foggiest how to go about that.