islower

Character classification macro.

Defined in header <ctype.h>

Syntax

#include <ctype.h>
int islower(int c);

Portability

Remarks

islower is a macro that classifies ASCII-coded integer values by table lookup. It is a predicate returning nonzero for true and 0 for false. It is defined only when isascii(c) is true or c is EOF.

You can make this macro available as a function by undefining (#undef) it.

Return value

islower returns nonzero if c is a lowercase letter {a to z).

Example

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

int main(void)
{
   char c = 'C';
   if (islower(c))
      printf("%c is lower case\n",c);
   else
      printfC'lc isn't lower case\n",c);
   return 0;

Differences from modern implementations

Nothing recorded yet.

Modern references

• cppreference (search)
• POSIX (search)
• Microsoft C runtime (search)

These are search links, not yet checked by hand.

Stable link: /3.1/ctype.h/islower/ · short form /3.1/islower/