Characters and Strings in C

Reading Character Data

C provides two equivalent approaches for reading individual characters.

• The C function getchar() reads and returns a single character.
  Example:

   
     char ch;
     ch = getchar();
  

• The c format for scanf reads an individual character.
  Example:

   
     char ch;
     scanf ("%c", &ch);
  

When reading character data with either getchar or %c with scanf, the first character is read and recorded; that is, the process of reading a character does NOT skip over white space.

Some of you may have noticed that Kernighan & Ritchie's book, The C Programming Language, declares int variables and sets them to char values, while the above examples declare char variables set to char values. The local system automatically converts the int values that getchar and getc into char values when set to a char variable, so on the local system, these declarations are valid. Just be aware that some systems may not support this automatic conversion.

Reading Strings

C also provides at least three approaches for reading strings of characters. Each function has its own special characteristics.

• The s format for scanf reads a sequence of non-white-space characters. As with all strings, a null character ('\0') is added at the end of the string.
  Example:

   
     char str[10];      /* allow room for 10 characters, including the null */
     scanf ("%s", str); /* since str is an array, the variable represents a
                           base address and no ampersand & is added */
  

• The C function gets() reads an entire line or until end of file. As with scanf, a null character is added at the end of the string.
  Example:

   
     char str[10];
     gets (str);     
  

• The C function fgets() reads up to n characters from a line or until end of file. As with scanf, a null character is added at the end of the string.
  Example:

   
     char str[10];             /* stdin is the C variable for "standard input" */
     fgets (str, 10, stdin);   /* up to 9 characters are read from the
                                  terminal, leaving room for a null character
                                  at the end */
                             
  

As with reading character data , stored input starts immediately with the first character read; the process of reading a string does NOT skip over white space.

Warning: Both scanf and gets read characters (until white space or the end of a line), without regard for the size of the string array. If more characters are read than fit in the array, the characters may overflow to fill data stored in other variables. Thus, only fgets can be considered "safe".