LinuxQuestions.org - C Language - For Loop that just keeps on runnin'

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Completely Clueless

08-01-2010 05:27 AM

C Language - For Loop that just keeps on runnin'

Hi guys,

In the code segment below is a for loop I am having some considerable difficulty with. It just keeps iterating endlessly and totally ignores the 70 times limit specified. I can't ever remember having this problem before and am absolutely Clueless. Can anyone spot the error?

Code:

for ( x = 0; x < 70; x++ )



{



  fputs ("CSN00", target);

  fprintf (target, "%d", userid);  

  fputc (',', target);



  fgets (usr, 9, users); 

  usr[8]=',';            

  fputs (usr, target);    

  



  fgets(pwd, 40, pass); 

  fputs(pwd, target);

  userid++;



 }

BTW, 'x' is declared as type 'int' earlier in the source.

Sergei Steshenko

08-01-2010 05:37 AM

Quote:

Originally Posted by Completely Clueless (Post 4051559)

Code:

for ( x = 0; x < 70; x++ )



{



  fputs ("CSN00", target);

  fprintf (target, "%d", userid);  

  fputc (',', target);



  fgets (usr, 9, users); 

  usr[8]=',';            

  fputs (usr, target);    

  



  fgets(pwd, 40, pass); 

  fputs(pwd, target);

  userid++;



 }

BTW, 'x' is declared as type 'int' earlier in the source.

How do you know the loop is running and how do you know how many times ?

Why won't print 'x' from inside the loop ?

Completely Clueless

08-01-2010 05:43 AM

Just inserted the printf x idea of yours and whilst the program runs, generating an increasingly large output file, x is stuck at only 4 for some reason. Any ideas?

Completely Clueless

08-01-2010 05:44 AM

I should say I don't have access to a IDE with a nice step-through de-bugger; I've only got nano!

Sergei Steshenko

08-01-2010 05:47 AM

Quote:

Originally Posted by Completely Clueless (Post 4051569)

Just inserted the printf x idea of yours and whilst the program runs, generating an increasingly large output file, x is stuck at only 4 for some reason. Any ideas?

Publish full source and compile with '-Wall -Wextra -Wformat=2' and make sure there are no warnings.

Completely Clueless

08-01-2010 05:50 AM

Ok, here's the complete source. In the mean time I will try your compile options...

Code:

#include <stdio.h>

#include <string.h>

#include <stdlib.h>



int main()



{



int x;

int userid=1;

char usr[8];    // array to store usernames

char pwd[40];  // array to store the passwords



 FILE *users; 



  users=fopen("users.txt", "r"); 

  if(users==NULL) 

    { 

    printf("Error: can't open file.\n"); 

    return 1; 

    } 



  FILE *pass; 



  pass=fopen("pass.txt", "r"); 

  if(pass==NULL) 

    { 

    printf("Error: can't open file.\n"); 

    return 1; 

    } 



  FILE *target; 



  target=fopen("target.csv", "w+"); 

  if(target==NULL) 

    { 

    printf("Error: can't create target file.\n"); 

    return 1; 

    } 



for ( x = 0; x < 70; x++ )



{



  fputs ("CSN00", target);

  fprintf (target, "%d", userid);  

  fputc (',', target);



  fgets (usr, 9, users);  // grabs first line of user file, including newline char

  usr[8]=',';            //overwrite the newline char with a comma

  fputs (usr, target);    

  



  fgets(pwd, 40, pass);  // might need some buffer flush perhaps

  fputs(pwd, target);

  userid++;

  printf ("%d",x);



 }





fclose (users);

fclose (pass);

fclose (target);



exit(0);



}

Completely Clueless

08-01-2010 05:53 AM

Your compile options generated no warnings or errors.

Sergei Steshenko

08-01-2010 05:55 AM

Quote:

Originally Posted by Completely Clueless (Post 4051573)

Ok, here's the complete source. In the mean time I will try your compile options...

Code:

#include <stdio.h>

#include <string.h>

#include <stdlib.h>



int main()



{



int x;

int userid=1;

char usr[8];    // array to store usernames

char pwd[40];  // array to store the passwords



 FILE *users; 



  users=fopen("users.txt", "r"); 

  if(users==NULL) 

    { 

    printf("Error: can't open file.\n"); 

    return 1; 

    } 



  FILE *pass; 



  pass=fopen("pass.txt", "r"); 

  if(pass==NULL) 

    { 

    printf("Error: can't open file.\n"); 

    return 1; 

    } 



  FILE *target; 



  target=fopen("target.csv", "w+"); 

  if(target==NULL) 

    { 

    printf("Error: can't create target file.\n"); 

    return 1; 

    } 



for ( x = 0; x < 70; x++ )



{



  fputs ("CSN00", target);

  fprintf (target, "%d", userid);  

  fputc (',', target);



  fgets (usr, 9, users);  // grabs first line of user file, including newline char

  usr[8]=',';             //overwrite the newline char with a comma

  fputs (usr, target);    

  



  fgets(pwd, 40, pass);  // might need some buffer flush perhaps

  fputs(pwd, target);

  userid++;

  printf ("%d",x);



 }





fclose (users);

fclose (pass);

fclose (target);



exit(0);



}

The item in red is wrong; compile should tell you so. Never compile without '-Wall -Wextra'.

Completely Clueless

08-01-2010 06:01 AM

Thanks, Sergei, but how does that cause the loop limit to be breached? And as I say, I am not getting any warnings at all with your option string.

Sergei Steshenko

08-01-2010 06:01 AM

Add -O2 - this will produce the needed warning.

Sergei Steshenko

08-01-2010 06:02 AM

Quote:

Originally Posted by Completely Clueless (Post 4051577)

Thanks, Sergei, but how does that cause the loop limit to be breached? And as I say, I am not getting any warnings at all with your option string.

I do not know whether this violation causes the problem; anyway, since your array and variables are on stack, violating array boundaries quite likely may cause broken variable value.

Completely Clueless

08-01-2010 06:04 AM

Quote:

Originally Posted by Sergei Steshenko (Post 4051580)

I do not know whether this violation causes the problem; anyway, since your array and variables are on stack, violating array boundaries quite likely may cause broken variable value.

Good point. I will look into it, thanks.

jay73

08-01-2010 06:05 AM

I get the impression you erased the \0 character terminating your string so fputs goes on printing forever because it doesn't know where to stop.

bigearsbilly

08-01-2010 06:06 AM

Quote:

Originally Posted by Completely Clueless (Post 4051571)

I should say I don't have access to a IDE with a nice step-through de-bugger; I've only got nano!

try this: ddd

it'll almost certainly be a package on your distro.

or sit down and learn how to use gdb

Completely Clueless

08-01-2010 06:21 AM

Quote:

Originally Posted by jay73 (Post 4051583)

I get the impression you erased the \0 character terminating your string so fputs goes on printing forever because it doesn't know where to stop.

Sounds distinctly possible. C# takes care of boundary-checking and the pesky NULL character automatically, I believe. Perhaps it's time I migrated!

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