Thread: input/output files

Well after fixing your syntax errors (you did not compile the above) the most glaring error was that you made a string buffer and never initialized it to zero. I did that before the loop and after each use:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main (void){


	FILE *inputFile;
	FILE *outputFile;

	char string[81];
	memset(string, 0, 81);

	int rowNr = 0;

	inputFile = fopen("test.txt", "r");
	outputFile = fopen ("nummering.txt", "w");

	while (fgets(string, 80, inputFile) != NULL){
		rowNr++;
		fprintf(outputFile, "%i %s\n", rowNr, string);
		memset(string, 0, 81);
	}		
	fclose (outputFile);
	fclose (inputFile);
	printf("\n");

	return 0;
}

Now your output file looks like:

Code:

jeff@jeff-gate:~/dev/crap$ gcc ./io.c -o iotest
jeff@jeff-gate:~/dev/crap$ ./iotest 

jeff@jeff-gate:~/dev/crap$ ls
nummering.txt
io.c    iotest   test.txt
jeff@jeff-gate:~/dev/crap$ cat ./nummering.txt 
1 Hello World.

2 How are you doing?

3 I am fine, thank you!

jeff@jeff-gate:~/dev/crap$

HTH...

Jeff

Luck: what you have when you read an unknown number of characters read into a char buffer and you try to use it as a string and nothing bad or inexplicable happens.

Peace of mind: Knowing beyond doubt that as long as your buffer is not overrun, you will have a terminating null.


I mentioned this in another thread but there are some C lib string functions that do NOT auto-magically append a terminating null to your string data. Here is but one:
http://www.cplusplus.com/reference/c...tring/strncpy/

And yes, you could have used your bytes_read return value to just stick a null at the end:

string[bytes_read] = '\0';

But if you are debugging stuff, the above way will show your buffer as <something like>:
[Hello05646332g veb rt7gh sscjfjdkbhaanbjk]

Whereas my method looks like:
[Hello000000000000000000000000000000]

Look I have just had to learn to code really defensively as some of the environments I have/had to code for are programmer-hostile (no monitor, no keyboard, etc) so everything you can do to bullet-proof the code (aka the belt and suspenders model) pays grand dividends.

For most toy/school projects this is probably overkill.

More voodoo programming.
Your memset serves NO purpose in this code.

fgets() ALWAYS terminates the buffer with a \0, unless fgets() itself returns NULL.