CODEWITHSUNDEEP
cfileio
Chris Gorman
Chris Gorman

Reputation: 195

What are some best practices for file I/O in C?

I'm writing a fairly basic program for personal use but I really want to make sure I use good practices, especially if I decide to make it more robust later on or something.

For all intents and purposes, the program accepts some input files as arguments, opens them using fopen() read from the files, does stuff with that information, and then saves the output as a few different files in a subfolder. eg, if the program is in ~/program then the output files are saved in ~/program/csv/

I just output directly to the files, for example output = fopen("./csv/output.csv", "w");, print to it with fprintf(output,"%f,%f", data1, data2); in a loop, and then close with fclose(output); and I just feel like that is bad practice.

Should I be saving it in a temp directory wile it's being written to and then moving it when it's finished? Should I be using more advanced file i/o libraries? Am I just completely overthinking this?

Upvotes: 6

Views: 3772

Answers (5)

Jens
Jens

Reputation: 72657

Best practices in my eyes:

  • Check every call to fopen, printf, puts, fprintf, fclose etc. for errors
  • use getchar if you must, fread if you can
  • use putchar if you must, fwrite if you can
  • avoid arbitrary limits on input line length (might require malloc/realloc)
  • know when you need to open output files in binary mode
  • use Standard C, forget conio.h :-)
  • newlines belong at the end of a line, not at the beginning of some text, i.e. it is printf ("hello, world\n"); and not "\nHello, world" like those mislead by the Mighty William H. often write to cope with the sillyness of their command shell. Outputting newlines first breaks line buffered I/O.
  • if you need more than 7bit ASCII, chose Unicode (the most common encoding is UTF-8 which is ASCII compatible). It's the last encoding you'll ever need to learn. Stay away from codepages and ISO-8859-*.

Upvotes: 9

user1732700
user1732700

Reputation:

You can make your own cat, cp, mv programs for practice.

Upvotes: 0

yatima2975
yatima2975

Reputation: 6610

If no other program is checking for the presence of ~/program/csv/output.csv for further processing, then what you're doing is just fine.

Otherwise you can consider writing to a FILE * obtained by a call to tmpfile in stdio.h or some similar library call, and when finished copy the file to the final destination. You could also put down a lock file output.csv.lck and remove that when you're done, but that depends on you being able to modify the other program's behaviour.

Upvotes: 0

teppic
teppic

Reputation: 8195

It's fine. I/O is fully buffered by default with stdio file functions, so you won't be writing to the file with every single call of fprintf. In fact, in many cases, nothing will be written to it until you call fclose.

It's good practice to check the return of fopen, to close your files when finished, etc. Let the OS and the compiler do their job in making the rest efficient, for simple programs like this.

Upvotes: 1

user529758
user529758

Reputation:

Am I just completely overthinking this?

You are. If the task's simple, don't make a complicated solution on purpose just because it feels "more professional". While you're a beginner, focus on code readability, it will facilitate your and others' lives.

Upvotes: 4

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