ifstream create new file

[vincec]

Hi i have a problem of ifstream creating new file when the file i want to open does not exist. According to some googling done, it does not create file. But i do not know why my program does. Is there any setting need to be done to prevent ifstream creating new files? Can help me.

Thanks a lot.

[Ganon11]

ifstream should not create new files, because it will be trying to load data from an existing file. To create a new, blank file would serve no purpose, since there would be no data to input.

You may be confused with ofstream. ofstream does create new files, since it will be saving data. It is perfectly all right to create a new, empty file if you know you are going to be filling the file with values rather than inputting values.

[vincec]

for (int x=0;x<2;x++)
    {
        for (int y=0;y<2;y++)
        {
        a.Format("%d",x);
        b.Format("%d",y);
        targetfilename = "PolyU_0" + a +"_" + b +".spmCHDHT";
 
        ifstream target(targetfilename);
 
        if(!target)
        {
            MessageBox("Cannot open file");
        }
        else
        {
            MessageBox("File opened");
        }
        }
 
    }

this is the code that i used. i tried using a new workspace to execute the code. it works, it will prompt some of the files "Cannot open file". But when i integrate it to the orginal file, ifstream will automatically create file. I think there must be some setting need or some #include file needed ?

[Ganon11]

Well, you would have to include <fstream>, but that's necessary for even using ifstream, so you probably already have it.

Try outputting targetfilename once you have set it and see what that is. I'm not sure what the .Format statements are doing, but it may be changing those values such that they no longer match your filename.

[vincec]

Hi thanks for helping, i have mange to solve the problem using fopen(); instead of ifstream. Using fopen, the program wouldn't create new file if the file i want to open for reading is not available. Although i still do not know why ifstream will create new file, but lucky that fopen did the job.

The .Format(); is for converting int to CString.