Question

I have a text file that I want to edit by rewriting it to a temp file and then overwrite the original. This code doesn’t do that as it’s simplified but it does include the problem I have. On Windows the EXAMPLE.TXT file will disappear after a seemly random number of runs when the rename function fails. I don’t know why but so far it has worked fine on Linux. Why does this happen and how can I solve it going in an entirety different direction, such as overwriting the original file from within the program without renaming?

Furthermore, what other, better methods exist? This method has other flaws on Windows, such as the program being closed by a user just after remove is called but before rename, which would not be a problem on Linux (after getting rid of remove)?

#include <stdio.h>
#include <assert.h>

int main(int argc, char *argv[]) {
  unsigned int i=0;
  FILE *fileStream, *tempStream;
  char fileName[] = "EXAMPLE.TXT";
  char *tempName = tmpnam(NULL);

  while(1) {
     printf("%u\n",i++);
     assert(fileStream = fopen(fileName, "r+"));
     assert(tempStream = fopen(tempName, "w"));

     fprintf(tempStream,"LINE\n");
     fflush(tempStream); /* fclose alone is enough on linux, but windows will sometimes not fully flush when closing! */

     assert(fclose(tempStream) == 0);
     assert(fclose(fileStream) == 0);
     assert(remove(fileName) == 0); /* windows fails if the file already exists, linux overwrites */
     assert(rename(tempName,fileName) == 0);
  }
}

Answer 1

Sometimes antivirus software can cause such a problem by scanning a file at an inconvenient moment.

If the remove fails, try sleeping for a short time and then retrying.