如果文件存在，请使用它；如果不存在，请创建它

问题描述：

fstream datoteka;
datoteka.open("Informacije.txt",  fstream::in | fstream::out | fstream::app);

if(!datoteka.is_open()){              
    ifstream datoteka("Informacije.txt")
    datoteka.open("my_file.txt", fstream::in | fstream::out | fstream::app);
}/*I'm writing IN the file outside of that if statement.

因此，如果以前未创建过文件，则应该创建一个文件，如果已创建，则将其写入该文件中.

So what it should do is create a file if it was not created before, and if it is created write into that file.

你好，所以我要从程序中检查文件是否已经存在，如果没有打开文件就可以打开程序，如果文件没有打开，我可以写入文件(还没有创建之前)创建程序.所以问题是当我创建一个.csv文件并完成写入时，我想检查写入的文件是否确实存在，无法打开该文件.在.txt文件中，所有内容均为空白.

Hello there, so what I wanted from my program is that it check if the file already exists, sothe program open if it does and I can write in it, if the file is not opened(have not been created before) the program create it. So the problem is when I create a .csv file, and finish writing and I wanted to check if the written is really there, the file cannot be opened. In .txt file, everything is blank.

答

datoteka.open(filename, std::fstream::in | std::fstream::out | std::fstream::app); 效果很好.

datoteka.open(filename, std::fstream::in | std::fstream::out | std::fstream::app); works fine.

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

int main(void)
{

     char filename[ ] = "Informacije.txt";
     fstream appendFileToWorkWith;

     appendFileToWorkWith.open(filename, std::fstream::in | std::fstream::out | std::fstream::app);


      // If file does not exist, Create new file
      if (!appendFileToWorkWith ) 
      {
        cout << "Cannot open file, file does not exist. Creating new file..";

        appendFileToWorkWith.open(filename,  fstream::in | fstream::out | fstream::trunc);
        appendFileToWorkWith <<"\n";
        appendFileToWorkWith.close();

       } 
      else   
      {    // use existing file
         cout<<"success "<<filename <<" found. \n";
         cout<<"\nAppending writing and working with existing file"<<"\n---\n";

         appendFileToWorkWith << "Appending writing and working with existing file"<<"\n---\n";
         appendFileToWorkWith.close();
         cout<<"\n";

    }




   return 0;
}

如果文件存在，请使用它；如果不存在，请创建它

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