Home/ Questions/Q 747307
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-14T14:11:23+00:00

For a particular piece of homework, I’m implementing a basic data storage system using

  • 0

For a particular piece of homework, I’m implementing a basic data storage system using sequential files under standard C, which cannot load more than 1 record at a time. So, the basic part is creating a new file where the results of whatever we do with the original records are stored. The previous file’s renamed, and a new one under the working name is created. The code’s compiled with MinGW 5.1.6 on Windows 7.

Problem is, this particular version of the code (I’ve got nearly-identical versions of this floating around my functions) doesn’t always remove the old file, so the rename fails and hence the stored data gets wiped by the fopen().

FILE *archivo, *antiguo;

remove("IndiceNecesidades.old");  // This randomly fails to work in time.
rename("IndiceNecesidades.dat", "IndiceNecesidades.old"); // So rename() fails.

antiguo = fopen("IndiceNecesidades.old", "rb");
// But apparently it still gets deleted, since this turns out null (and I never find the .old in my working folder after the program's done).
archivo = fopen("IndiceNecesidades.dat", "wb"); // And here the data gets wiped.

Basically, anytime the .old previously exists, there’s a chance it’s not removed in time for the rename() to take effect successfully. No possible name conflicts both internally and externally.

The weird thing’s that it’s only with this particular file. Identical snippets except with the name changed to Necesidades.dat (which happen in 3 different functions) work perfectly fine. 

// I'm yet to see this snippet fail.
FILE *antiguo, *archivo;

remove("Necesidades.old");
rename("Necesidades.dat", "Necesidades.old");

antiguo = fopen("Necesidades.old", "rb");
archivo = fopen("Necesidades.dat", "wb");

Any ideas on why would this happen, and/or how can I ensure the remove() command has taken effect by the time rename() is executed? (I thought of just using a while loop to force call remove() again so long as fopen() returns a non-null pointer, but that sounds like begging for a crash due to overflowing the OS with delete requests or something.)

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    So suddenly, after reading Scott’s mention of permissions, I thought about “Permission Denied” and applied some Google. Turned out it’s a pretty common, if obscure, error.
    caf was right, it was in another piece of code. Namely, I had forgotten to fclose that same file in the function meant to show the contents. Since I wasn’t tracking that particular detail, it appeared to be random.

    Disclaimer: Weekly math assigments make for very little sleeptime. ¬¬

    • 0