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02-09-2010, 01:01 PM
| #1 |
| Registered User Join Date: Feb 2010
Posts: 74
| input/output files I have been playing with input & outputfiles in C. But I get to much information in my outputfile and I dont know why. Im using a mac. This is my code : Code: #include <stdio.h>
#include <stdlib.h>
int main (void){
FILE *inputFile;
FILE *outputFile;
char string[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);
}
fclose (outputFile);
fclose (inputFptr);
printf("\n");
return 0;
}
Hello World. How are you doing? I am fine, thank you! This is the output file: 1 {\rtf1\ansi\ansicpg1252\cocoartf1038\cocoasubrtf25 0 2 {\fonttbl\f0\fswiss\fcharset0 Helvetica;} 3 {\colortbl;\red255\green255\blue255;} 4 \paperw11900\paperh16840\margl1440\margr1440\vieww 9000\viewh8400\viewkind0 5 \pard\tx566\tx1133\tx1700\tx2267\tx2834\tx3401\tx3 968\tx4535\tx5102\tx5669\tx62 6 36\tx6803\ql\qnatural\pardirnatural 7 8 \f0\fs24 \cf0 Hello World.\ 9 How are you doing?\ 10 I am fine, thank you!\ 11 \ 12 } |
| thescratchy is offline |  |
|
02-09-2010, 01:10 PM
| #2 |
| Robot Join Date: Mar 2009
Posts: 372
| Your "text file" is actually a RTF file. The Mac OS X text editor saves in that format by default. |
| Memloop is offline | |
|
02-09-2010, 01:16 PM
| #3 |
| Registered User Join Date: Feb 2010
Posts: 74
| Thank you very much saved it as plain text and its ok now. |
| thescratchy is offline | |
|
02-09-2010, 01:29 PM
| #4 |
| Registered User  Join Date: Dec 2009 Location: Henderson, NV
Posts: 887
| 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;
}
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$ Jeff |
| jeffcobb is offline | |
|
02-09-2010, 01:37 PM
| #5 |
| Registered User Join Date: Feb 2010
Posts: 74
| Wy do you initiliaze the string everytime? What happens if you dont do it? Because it worked without the initializing. |
| thescratchy is offline | |
|
02-09-2010, 01:45 PM
| #6 |
| Registered User Join Date: Dec 2009 Location: Henderson, NV
Posts: 887
| 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/ |
| jeffcobb is offline | |
|
02-09-2010, 01:50 PM
| #7 |
| Registered User Join Date: Dec 2009 Location: Henderson, NV
Posts: 887
| 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] |
| jeffcobb is offline | |
|
02-09-2010, 01:54 PM
| #8 |
| Registered User Join Date: Dec 2009 Location: Henderson, NV
Posts: 887
| 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. |
| jeffcobb is offline | |
|
02-09-2010, 03:35 PM
| #9 |
| and the hat of Destiny  Join Date: Aug 2001 Location: The edge of the known universe
Posts: 22,495
| More voodoo programming. Your memset serves NO purpose in this code. fgets() ALWAYS terminates the buffer with a \0, unless fgets() itself returns NULL. |
| Salem is offline | |
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