String Validation

[duvernais28]

Can anybody give me a simple example of a string validation whereby I would validate a string of chars. I checked through the Faqs but it was a little bit over my head.
Nb: I am comfortable with fgets, sscanf, etc. With typedef, enum, and static, well, I'm still getting there.
Your help would be very much appreciated.

[sean]

What do you mean by validate? Would strcmp meet your needs? If you're interested in working with strings have a look at http://www.infosys.utas.edu.au/info/...C/CStdLib.html and browse through string.h. strtok is another one you might be interested in using. You specify a "delimiting" character, and when used in a loop, it will separate out all the "substrings" spearated by that character. It's operation is a tad complicated, so make sure you understand what it does to the string before you use it. If you need help PM me and I'll explain how it works.

[Kleid-0]

Here's an example:

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>       // imports isalpha(), isdigit(), etc...

// String validation; In the form of:
// [alpha][number][alpha] aka: a3e r2q
int main( void )
{
  // Input string

  char sz[4];

  // Get input

  fgets( sz, sizeof( sz ), stdin );

  // Output input

  printf( "You entered: %s\n", sz );

  // Validate input

  if( isalpha( sz[0] ) && isdigit( sz[1] ) && isalpha( sz[2] ) )
    puts( "Good form" );
  else
    puts( "Bad form, bad!" );

  // Successfully exit

  return 0;
}

[andyhunter]

If you need help PM me and I'll explain how it works.

sean - hey you and a couple of others have been saying this quite a bit on various posts. Doesn't it help the greater good to have this discussion on the thread vice existing in PMs? Just asking a question.

-Andy

[sean]

Good point, but who knows if I'll ever look at this thread again?

[duvernais28]

Thanks alot guys. The best solution I've seen so far is from Kleid-0. strtok() would not be very useful bcos there would be too many characters to delimit. My intention is to validate that an array is composed of alphas only.

[duvernais28]

Hey Andy. I'm a bit new here, still trying to navigate my way around. I have no idea of how to send PMs in this forum yet

[sean]

Click on User CP in the top-left-hand corner.

[Dave_Sinkula]

My intention is to validate that an array is composed of alphas only.

#include <stdio.h>
#include <ctype.h>

int alpha_only ( const char *s )
{
   if ( !*s )
   {
      return 0;
   }
   for ( ; *s; ++s )
   {
      if ( !isalpha ( *s ) )
      {
         return 0;
      }
   }
   return 1;
}

int main ( void )
{
   const char *text[] = 
   {
      "AlphasOnly",
      "abc123",
      "",
      "123abc",
      "1a2b3c",
      "Hello world",
   };
   size_t i;
   for ( i = 0; i < sizeof text / sizeof *text; ++i )
   {
      printf("\"%s\" : %s\n", text [ i ], 
             alpha_only ( text [ i ] ) ? "yes" : "no" );
   }
   return 0;
}

/* my output
"AlphasOnly" : yes
"abc123" : no
"" : no
"123abc" : no
"1a2b3c" : no
"Hello world" : no
*/

[duvernais28]

Good job Dave. Thanks alot.

[duvernais28]

Dave, I tried your example and it works fine. However, I'm having alot of trouble adopting this to a string that is inputed by the user. Actually, all my attempts to adapt it have ended with the program crashing. I would appreciate it if anyone could help me out with this one.

[andyhunter]

Well, show your latest attempt and I will be glad to help.

[duvernais28]

Well, bro. I know you won't believe me on this one but the truth is I scrapped it. I can tell you what my results were though. After removing the string data in the text array and initializing it at BUFZIZ. I used fgets to input a string and then attempted to printf the same string making use of the alpha_only function. The program crashed as son as it compiled. I also attempted to initialise the text array as a normal char. It still crashed on compiling. I use boland c++ builderX so on compiling the program runs imediately.

You may still not believe that I've tried anything but the truth is that I scrapped it. I honestly would not come here and ask questions without working on what I've been given.

[andyhunter]

Alright, I'll give you the benefit of the doubt. Here is how I percieved the answer:

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


void getLine(char**);
int validate(char*);

int main ( void )
{
   char* text = NULL; 
   
   printf("Enter a string: ");
   getLine(&text);

   printf("%s - %s \n", text, validate(text) ? "yes" : "no");

   return 0;
}
void getLine(char** message) {

    int ch, len = 0;

    while((ch = getchar()) != '\n') { //check for end of line
        *message = (char*)realloc(*message, len+1); //increase inputString by 1 char
        if(*message == NULL) {
            puts("Error allocating memory");
            exit(1);
        }
        (*message)[len++] = ch;
    }
    (*message)[len] = '\0'; //add end token
}
int validate(char* s) {

    for(int i =0; i < strlen(s); i++) {

        if(!isalpha(s[i])) 
            return 0;
    }

    return 1;
}

If you have any questions let me know.

[duvernais28]

Thanks alot Andy. Your solution works fine apart from 'i' needing to be declared
before/outside the for() condition. However, I suspect that I may need to slow down here. I'm working on this project and I have gone way beyond my the study guide I was given so far. I have been able to validate all other fields in my project so far and I have only one week to complete it. I see no way for me to properly learn pointers, memory allocations, and any other data types in such a short time and complete this project(with documentation) in one week. And there will be no point in using what I don't understand.

I'll definitely be looking into the solutions that I've seen here but at a slower pace. I know that I've already passed this course.

Thanks alot to all you guys who helped me out