Planet For Application Life Development Presents
MY IT World

Explore and uptodate your technology skills...

C - Strings

What is a String?

Note that along with C-style strings, which are arrays, there are also string literals, such as "this". In reality, both of these string types are merely just collections of characters sitting next to each other in memory. The only difference is that you cannot modify string literals, whereas you can modify arrays. Functions that take a C-style string will be just as happy to accept string literals unless they modify the string (in which case your program will crash). Some things that might look like strings are not strings; in particular, a character enclosed in single quotes, like this, 'a', is not a string. It's a single character, which can be assigned to a specific location in a string, but which cannot be treated as a string. (Remember how arrays act like pointers when passed into functions? Characters don't, so if you pass a single character into a function, it won't work; the function is expecting a char*, not a char.)
strings are arrays of chars. String literals are words surrounded by double quotation marks.

"This is a static string"
char string[50];

This would declare a string with a length of 50 characters. Do not forget that arrays begin at zero, not 1 for the index number. In addition, we've accounted for the extra with a null character, literally a '\0' character. It's important to remember that there will be an extra character on the end on a string, just like there is always a period at the end of a sentence. Since this string terminator is unprintable, it is not counted as a letter, but it still takes up a space. Technically, in a fifty char array you could only hold 49 letters and one null character at the end to terminate the string.

Using Strings

Strings are useful for holding all types of long input. If you want the user to input his or her name, you must use a string. Using scanf() to input a string works, but it will terminate the string after it reads the first space, and moreover, because scanf doesn't know how big the array is, it can lead to "buffer overflows" when the user inputs a string that is longer than the size of the string (which acts as an input "buffer").

#include <stdio.h>

int main()
    /* A nice long string */
    char string[256];                               

    printf( "Please enter a long string: " );

    /* notice stdin being passed in */
    fgets ( string, 256, stdin );           

    printf( "You entered a very long string, %s", string );


Manipulating C strings using string.h

string.h is a header file that contains many functions for manipulating strings. One of these is the string comparison function.

#include <stdio.h>    /* stdin, printf, and fgets */
#include <string.h>   /* for all the new-fangled string functions */

/* this function is designed to remove the newline from the end of a string
entered using fgets.  Note that since we make this into its own function, we
could easily choose a better technique for removing the newline.  Aren't
functions great? */
void strip_newline( char *str, int size )
    int i;

    /* remove the null terminator */
    for (  i = 0; i < size; ++i )
        if ( str[i] == '\n' )
            str[i] = '\0';

            /* we're done, so just exit the function by returning */
    /* if we get all the way to here, there must not have been a newline! */

int main()
    char name[50];
    char lastname[50];
    char fullname[100]; /* Big enough to hold both name and lastname */

    printf( "Please enter your name: " );
    fgets( name, 50, stdin );

    /* see definition above */
    strip_newline( name, 50 );

    /* strcmp returns zero when the two strings are equal */
    if ( strcmp ( name, "Alex" ) == 0 ) 
        printf( "That's my name too.\n" );
        printf( "That's not my name.\n" );
    // Find the length of your name
    printf( "Your name is %d letters long", strlen ( name ) );
    printf( "Enter your last name: " );
    fgets( lastname, 50, stdin );
    strip_newline( lastname, 50 );
    fullname[0] = '\0';            
    /* strcat will look for the \0 and add the second string starting at
       that location */
    strcat( fullname, name );     /* Copy name into full name */
    strcat( fullname, " " );      /* Separate the names by a space */
    strcat( fullname, lastname ); /* Copy lastname onto the end of fullname */
    printf( "Your full name is %s\n",fullname );


    return 0;