What is wrong with this C code?

daYz · 08-13-2007, 02:43 PM

Hi,

Can someone tell me what is wrong with the following code please? I am trying to write a program that downloads the newest version of a program that is available on a server. The code searches trough apache.txt wich contains a directory listing of a server. When it finds a match it should print out buff, but for some reason this does not work as intended. If a match is found the program continues to look for a higher version in the next for loop.
The "i != 200" will need to be replaced with something like "! fseek(fptr, i, SEEK_SET) == 0" so that the program will end when the end of the file has been reached but I have not had the oppurtunity yet to take a look at that.

Thanks for your help

Code:

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


char httpd[] = "httpd-2.2.3.tar.bz2";

char buff[20];

int k = 4;

int i;



int main()
{

FILE *fptr;

fptr = fopen("apache.txt", "r");



for ( i=0; i != 200; k++){

        do {
		fseek(fptr, i, SEEK_SET);
                i++;
		fgets(buff,20,fptr);
		
        } while ( ! strcmp(httpd, buff) == 0 );


printf("%s" is found, buff);

i = ftell(fptr);

char num[3];
sprintf(num,"%d",k);
httpd[10] = num[0];
}

fclose(fptr);


return 0;

}

SciYro · 08-13-2007, 02:50 PM

Umm, why are you using "!= 200", its most probably that when 'i' is 200, it will not enter the for loop, but continue to increase in the while loop, so the for loop will never exit. Might want to have a exit clause in the for loop, or replace "!=" with a greater or less then comparison.

Speaking for which, i dont see why you even have 2 nested loops just to find a single line in a single file. Why not use a while loop that ends when end of file is reached, with a if statement to check if you have the correct line, and break out of the loop then?

daYz · 08-13-2007, 03:31 PM

Quote:

Umm, why are you using "!= 200", its most probably that when 'i' is 200, it will not enter the for loop, but continue to increase in the while loop, so the for loop will never exit. Might want to have a exit clause in the for loop, or replace "!=" with a greater or less then comparison.

Thanks for your reply. I have changed "!= 200" to "<= 200", but it does not get my code working yet, unfortunately.

Quote:

Speaking for which, i dont see why you even have 2 nested loops just to find a single line in a single file. Why not use a while loop that ends when end of file is reached, with a if statement to check if you have the correct line, and break out of the loop then?

I did not think of this yet. I am going to try this out. That should also work indeed.

reverse · 08-14-2007, 01:43 AM

Code:

printf("%s" is found, buff);

Chnage it to: printf("%s is found", buff);

--

I think you'd be better off with a shell script. Pick the best tool for the job.

daYz · 08-14-2007, 06:31 AM

Quote:

Originally Posted by reverse

Code:

printf("%s" is found, buff);

Chnage it to: printf("%s is found", buff);

--

I think you'd be better off with a shell script. Pick the best tool for the job.

Thanks reverse.

I have considered writing the program partially in Bash, but I decided to write it fully in C so I could learn from it because I am just starting out with the language.

The following code is a working replacement of the code I provided earlier, but can someone tell me with what statement I can replace

Code:

i < 500

, so that the for loop ends when a end of file is reached, and not when i will be equal or greater than 500..

Code:

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


char httpd[] = "httpd-2.2.3.tar.bz2";

char buff[20];


int i;

int k = 3;


int main()
{

FILE *fptr;

fptr = fopen("apache.txt", "r");



for ( i=0; i < 500; i++){


		fseek(fptr, i, SEEK_SET);
		fgets(buff,20,fptr);
		
         if ( strcmp(httpd, buff) == 0 ){

printf("%s is found\n\n", buff);
k++;
i = ftell(fptr);
i--;

char num[3];
sprintf(num,"%d",k);
httpd[10] = num[0];

} 
}

fclose(fptr);


return 0;

}

Thanks

SciYro · 08-14-2007, 08:51 PM

relpace with "; ;" should do:

Code:

// forgive the non-tabed indents, cant get firefox to allow me to press "tab" and work


for (unsigned int i = 0; ; i++) {
   fseek(fptr, i, SEEK_SET);
   if (fgets(buff,20,fptr) == -1)
      break; // read error, EOF probably
   if (strcmp(httpd, buff) == 0) {
      printf("%s is found at %i\n\n", buff, i);
      break; // stop searching upon first find
   }
}

daYz · 08-15-2007, 09:22 AM

Thanks SciYro