Cannot open a file in C- Error in opening a file in C

Question

The main function that opens the file is located in "project" directory. Then I have a "cmake-build-bug" directory( located in "project" directory) where is "data.txt" file located. I want to read it, but for some reason it keeps wrinting Error to open file. I never understand how to write the correct path to the file. Or is there another problem that gives the error?

  FILE *file[2] ;
  char *fileName2 = "data.txt";
    file[1] = fopen(fileName2, "r");
    if (file[1] == NULL){
        printf("Error to open file
");
    }
        printf("Reading..
");
  fclose(file[1]);

Answer 1

When using an IDE (and since you have a cmake-build-debug directory then I guess you're using the CLion IDE) the default working directory is seldom what is expected. And for CLion it seems it's not where you currently store the data.txt file. (I don't remember the default for CLion.)

Assuming CLion, you need to edit your "Run/Debug Configuration" for the program (menu "Run" and item "Edit Configuration"), and set the "Working Directory" to where you have the data.txt file.