Sams Teach Yourself C in 21 Days

Manipulating Strings 501

17

String Conversions ..............................................................................................

Many C libraries contain two functions that change the case of characters within a string.

These functions aren’t ANSI standard and, therefore, might differ or not even exist in

your compiler. Because they can be quite useful, they are included here. Their proto-

types, in string.h, are as follows for the Microsoft C compiler (if you use a different com-

piler, they should be similar):

char *strlwr(char *str);

char *strupr(char *str);

The function strlwr()converts all the letter characters in strfrom uppercase to lower-

case;strupr()does the reverse, converting all the characters in strto uppercase.

Nonletter characters aren’t affected. Both functions return str. Note that neither function

actually creates a new string, but both modify the existing string in place. Listing 17.13

demonstrates these functions. Remember that to compile a program that uses non-ANSI

functions, you might need to tell your compiler not to enforce the ANSI standards.

LISTING17.13 upper.c. Converting the case of characters in a string with strlwr()and

strupr()

1: /* The character conversion functions strlwr() and strupr(). */

2:

3: #include <stdio.h>

4: #include <string.h>

5:

6: int main( void )

7: {

8: char buf[80];

9:

10: while (1)

11: {

12: puts(“Enter a line of text, a blank to exit.”);

13: gets(buf);

14:

15: if ( strlen(buf) == 0 )

16: break;

17:

18: puts(strlwr(buf));

19: puts(strupr(buf));

20: }

21: return 0;

22: }

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