C ++读取应该已经存在的输出文件

Question

如何提示用户输入输出文件名和IF not found 重试？

每次发生这种情况时，它都会创建输出文件；我不希望我只希望它读取输出文件。

do{
cout <<"Type the name of the output file which will hold the simulation             results:\n";
cin >> nameoutputfile;
fileout.open(nameoutputfile);

if (fileout.fail())
{
cout << "ERROR: File "<< nameoutputfile <<" could not be opened\n";
tries[1]++;
}
if (tries[1] == trylimit)
{
cout << "ERROR: You exceeded maximum number of tries allowed\n";
cout << "while entering the input file name";
return 2;
}
}while(fileout.fail());

这就是输出应该是什么

outputReadOnly.txt   
ERROR: File outputReadOnly.txt could not be opened    
Type the name of the output file which will hold the simulation results:  
outputReadOnly.txt  
ERROR: File outputReadOnly.txt could not be opened  
Type the name of the output file which will hold the simulation results:  
outputReadOnlyt.txt  
ERROR: You exceeded maximum number of tries allowed  
while entering the output file name 

Answer 1

看起来您正在使用ofstream fileout;，默认情况下会覆盖现有文件。要实现所需的行为，您可以使用 fstream 并指定两个 in | out 标志：

fstream fileout;
do{
  // Other code skipped for simplicity
  fileout.open(nameoutputfile, ios_base::in|ios_base::out);
  // ...
}while(fileout.fail());

这是fstream.open使用的默认标志，所以你可以写：

fileout.open(nameoutputfile);