Skip to main content

How String Functions (string.h) Work?

In the previous article String Manipulation Functions (string.h), we had a look at some of the commonly used string manipulation functions. There is no denying the fact that those functions are useful but have you ever wondered how those functions actually work or what is the algorithm behind their working?

If yes then read on…

In this article I am going to present you with our own version of the string manipulation functions that we had discussed, namely strlen(), strcpy(), strcat() and strcmp(). Our versions will do the same thing as done by the original functions but surely they would teach us a lot!

Let's have a look at them one-by-one:

mystrlen

  // mystrlen- function 
  #include<iostream.h>

  int mystrlen(const char *);

  void main(void)
  {
   char ch[]="This is great!";
   cout<<"Length:"<<mystrlen(ch);
  }

  int mystrlen(const char *str)
  {
   int len=0;

   while(str[len]!='\0')
     len++;
   return len;
  }

mystrcpy

  // mystrcpy- function 
  #include<iostream.h>

  void mystrcpy(char *,const char *);

  void main(void)
  {
   char ch[]="This is great!";
   char ch2[20];

   mystrcpy(ch2,ch);

   cout<<ch;
   cout<<endl;
   cout<<ch2;
  }

  void mystrcpy(char *str1,const char *str2)
  {
   int i=0;

   // copy each character
   while(str2[i]!='\0')
   {
    str1[i]=str2[i];
    i++;
   }
   // put the end of 
   // string identifier
   str1[i]='\0';
  }

mystrcat

  // mystrcat- function 
  #include<iostream.h>

  void mystrcat(char *,const char *);

  void main(void)
  {
   char ch[]="This is great!";
   char ch2[25]="Yes ";

   mystrcat(ch2,ch);

   cout<<ch;
   cout<<endl;
   cout<<ch2;
  }

  void mystrcat(char *str1,const char *str2)
  {
   int i=0;
   int len=0;

   // skip to the end of the first
   // string(target)
   while(str1[len]!='\0')
     len++;

   // start copying characters
   // from the start of the 
   // second string (source)
   // to the end of the
   // first (target)
   while(str2[i]!='\0')
   {
    str1[len]=str2[i];
    i++;len++;
   }
   str1[len]='\0';
  }

mystrcmp

  // mystrcmp- function
  #include<iostream.h>

  int mystrcmp(char *,const char *);

  void main(void)
  {
   char ch[]="C++";
   char ch2[]="C++";

   cout<<mystrcmp(ch2,ch);
  }

  int mystrcmp(char *str1,const char *str2)
  {
   int i=0,cmp=-1;

   while(str1[i]!='\0')
   {
    if(str1[i]==str2[i])
    {
     // check one character
     // following it, so that
     // end of string is also
     // compared
     if(str1[i+1]==str2[i+1])
       cmp=0;
     // if not same then check
     // to see which string has 
     // higher ASCII value for the
     // non-matching charcter
     else if(str1[i+1]<str2[i+1])
     {
      cmp=-1;
      break;
     }
     else
     {
      cmp=1;
      break;
     }
    }
    else if(str1[i]<str2[i])
    {
     cmp=-1;
     break;
    }
    else
    {
     cmp=1;
     break;
    }
    i++;
   }
   return cmp;
  }

Good-Bye!

Related Articles:

Labels:

Popular posts from this blog

The Best Way(s) to Comment out PHP/HTML Code

PHP supports various styles of comments. Please check the following example: <?php // Single line comment code (); # Single line Comment code2 (); /* Multi Line comment code(); The code inside doesn't run */ // /* This doesn NOT start a multi-line comment block /* Multi line comment block The following line still ends the multi-line comment block //*/ The " # " comment style, though, is rarely used. Do note, in the example, that anything (even a multi-block comment /* ) after a " // " or " # " is a comment, and /* */ around any single-line comment overrides it. This information will come in handy when we learn about some neat tricks next. Comment out PHP Code Blocks Check the following code <?php //* Toggle line if ( 1 ) {      // } else {   ...
Read more

How to Create an HTML Form Linked with MySQL Database in PHP

If you're looking for example code and detailed discussion on how to create an HTML form that stores data in a MySQL database using PHP then this post might be what you're looking for. I assume that you're familiar with basic HTML, CSS, PHP coding, and  MySQL. I am going to divide this small project into two parts: The HTML form itself that takes input from the user and the PHP script that saves it into the database A table that displays the user-added data that has been saved in the database. We'll be dealing with the first part in this tutorial. Again I'd like to break this problem into a few parts so that it's easier for you to understand and probably gives you an insight into how breaking up a problem into smaller chunks can help make things clearer in your mind. Let's think about it, there is an HTML form (that is HTML code), then there is the PHP code that deals with the user-input data, and the MySQL database itself. For this tutorial, we'll b...
Read more

Fix For Toshiba Satellite "RTC Battery is Low" Error (with Pictures)

RTC Battery is Low Error on a Toshiba Satellite laptop "RTC Battery is Low..." An error message flashing while you try to boot your laptop is enough to panic many people. But worry not! "RTC Battery" stands for Real-Time Clock battery which almost all laptops and PCs have on their motherboard to power the clock and sometimes to also keep the CMOS settings from getting erased while the system is switched off.  It is not uncommon for these batteries to last for years before requiring a replacement as the clock consumes very less power. And contrary to what some people tell you - they are not rechargeable or getting charged while your computer or laptop is running. In this article, we'll learn everything about RTC batteries and how to fix the error on your Toshiba Satellite laptop. What is an RTC Battery? RTC or CMOS batteries are small coin-shaped lithium batteries with a 3-volts output. Most laptops use ...
Read more