Help in checking password in a file

Quote:

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Originally Posted by matsp

Well, the "example" would depend on what you need to do in "validating the input". For example, if you are asking for a username that is supposed to be 20 chars long, then you may do something like:

Code:

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    char temp[BUFSIZ];
    char username[21] = "!!InvalidUser!!";  // Make a default name that can't be used
    printf("Username: ");
    if (fgets(temp, BUFSIZ, stdin) != NULL)
    {
      // Remove newline if it's there.
      if (temp[strlen(temp)-1]  == '\n')
          temp[strlen(temp)-1] = 0;
      if (strlen(temp) > sizeof(username)-1)  { 
            /// username is too long  - tell user, or just ignore it [leaving the "default" invalid name in there].
      } else {
          strcpy(username, temp);
      }
    }
    ...

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Mats

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i don understand one thing...

since i declared the array size of the inputted user name is the same as the username inside the file...would that be a problem why would i need BUFSIZE?

how are your string functions even working without

#include <string.h>

Quote:

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Originally Posted by JFonseka

how are your string functions even working without

#include <string.h>

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i don know....when i compile there are no errors or warnings.

now added string.h already, the problem still persist...

it seems the linebuffer parsing more than 3 fields....i don know why is like that.

Or it's not getting exactly three - why not add a debug print to print out the result from scanf() when it's not three. [I find it unlikely that it says more than three].

If you are not getting any warnings if you are not including string.h - you probably aren't using "-Wall" on the compiler line - and thus the warnings aren't enabled, rather than "there aren't any".

--
Mats

Quote:

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Originally Posted by matsp

Or it's not getting exactly three - why not add a debug print to print out the result from scanf() when it's not three. [I find it unlikely that it says more than three].

If you are not getting any warnings if you are not including string.h - you probably aren't using "-Wall" on the compiler line - and thus the warnings aren't enabled, rather than "there aren't any".

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Mats

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how to add a debug print? can show me how?

Quote:

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Originally Posted by frodonet

how to add a debug print? can show me how?

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A "debug print" is [in this case] just a printf() to print the result variable from your scanf inside the "if ( ... != 3)" side. I think you are capable of doing that without an example - if you are not, you need to go back a few steps and read the first couple of chapters in your C book again.

There is, in large systems, a case of "debug logging", which is generally that the application contains a set of functions, and calls to those functions, to print "useful stuff" when you enable debugging - so you don't have to recompile the application with different code, it already has such code built into it. It usually also invovles different debug levels or debug flags, so you can for example enable logging at "low volume" [debuglevel=1] or "a bit more" [debuglevel=2] or "everything available" [debuglevel=1000]. Or you can have "debug main" [set bit 0 of debugflags] "debug module 1" [set bit 1 of debugflags], "debug module 5", [set bit 5 of debugflags]. If you set debugflags to all ones, you [obviously] get all debug output.

But in your case, the applicaton is small, and easy to change, so just adding and removing the debug output would be the right thing to do.

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Mats

Guys, this is the latest development i did on my program.

i compiled it in bloodshed C++..no warnings or whatsoever...

but still the line buffer has more than 3 fields...which i think causing the problem...

but i don see where the problem is and why it has more than 3 fields...

can anyone see where i did wrong??

this is just one part of my program, i still have the 2nd and 3rd part...and help would be appreciated cause if haven't settle this first one, i can;t go with the 2 and 3 part.:(

Code:

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

main( )
 {
    FILE *fpassword;
    char line_buffer[100], pass[20], user[20];
    fpassword = fopen("C:\\PASSWD.TXT", "r");
    if (fpassword == NULL) printf("File doesn't exist\n");

    printf("Userid: ");
    fgets(user,sizeof(user),stdin);

    printf("Password: ");
    fgets(pass,sizeof(pass),stdin);

    while( fgets(line_buffer,sizeof(line_buffer),fpassword) != NULL )  /* read from file while still data available */
    {
            char ftemp[20], fpass[20], fuser[20];
            if( sscanf(line_buffer,"%.20s %.20s %.20s",ftemp,fpass,fuser) != 3 )  /* Make sure we parsed 3 fields from the line */
            {
                printf("here's the problem");
                getch();
                exit(1);

            }
            else /* Otherwise, we got 3 fields */
            {
                  if (strcmp(user, fuser) == 0) /* OK, found the username the user inputted */
                    {
                          if (strcmp(pass, fpass) == 0) /* Now, check if passwords match, if they do not, user entered a faulty password */
                      {
                                  printf("User authorized");
                          getch();
                          exit(1);
                      }
                          else
                      {
                                  printf("User not authorized");
                          getch();
                          exit(1);
                      }
                    }
            }

      }

    fclose(fpassword);
    getchar();
 }

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Why don't you move the scanf out of the if, and assign the result to a variable so that you can print the number it actually got, along with the input line that you are trying to scanf()?

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Mats

Another note: your program doesn't quit if it can't open the file - it simply says an error and continues to execute the program.

Code:

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while( fgets(line_buffer,sizeof(line_buffer),fpassword) != NULL )  /* read from file while still data available */
    {
            char ftemp[20], fpass[20], fuser[20];
            printf("%s,%s", user, pass);
            sscanf(line_buffer,"%s %s %s",&ftemp,&fpass,&fuser);  /* Make sure we parsed 3 fields from the line */
            printf("%s,%s,%s\n", ftemp, fpass, fuser);
            getch();
            exit(1);
      }

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hi matxp, i've done what you say...

this is the output...

http://i147.photobucket.com/albums/r...untitled-9.jpg

Quote:

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Originally Posted by Elysia

Another note: your program doesn't quit if it can't open the file - it simply says an error and continues to execute the program.

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but earlier before i do scanf i have put these command.

Code:

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fpassword = fopen("C:\\PASSWD.TXT", "r");
if (fpassword == NULL) printf("File doesn't exist\n");

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but if it can't open in the first place...shouldn't it terminate instantly?? rather than continue executing...

Doh!

You are passing in string pointers with & - remove the & and you should be fine. [At least I think so]. Since the strings are arrays, they are already passed as the address of the data.

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Mats

QUOTE=frodonet;683665]but earlier before i do scanf i have put these command.

Code:

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fpassword = fopen("C:\\PASSWD.TXT", "r");
if (fpassword == NULL) printf("File doesn't exist\n");

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but if it can't open in the first place...shouldn't it terminate instantly?? rather than continue executing...[/QUOTE]

Well, there's probably no point in continuing, is there? If you DO continue, you will need to check if fpassword is not NULL before you read from it, that's for sure. And what DO you do if you can't read the file?

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Mats

Quote:

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Originally Posted by matsp

Doh!

You are passing in string pointers with & - remove the & and you should be fine. [At least I think so]. Since the strings are arrays, they are already passed as the address of the data.

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Mats

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hahah...i remove the '&' and the output came correct, one question though...

why i did a printf on my password entered...it has a coma in front it? why?

Quote:

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Originally Posted by frodonet

hahah...i remove the '&' and the output came correct, one question though...

why i did a printf on my password entered...it has a coma in front it? why?

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Because there is a newline at the end of "John1" that is printed as part of the username, then a comma after the username, which comes out on the next line, before the password. You probably want to remove those. I posted a post earlier about how to remove the newline after fgets().

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Mats