This section explains the library functions for performing conversions
such as case mappings on characters. For example, toupper
converts any character to upper case if possible. If the character
can’t be converted, toupper returns it unchanged.
These functions take one argument of type int, which is the
character to convert, and return the converted character as an
int. If the conversion is not applicable to the argument given,
the argument is returned unchanged.
Compatibility Note: In pre-ISO C dialects, instead of
returning the argument unchanged, these functions may fail when the
argument is not suitable for the conversion. Thus for portability, you
may need to write islower(c) ? toupper(c) : c rather than just
toupper(c).
These functions are declared in the header file ctype.h.
int tolower (int c) ¶Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.
If c is an upper-case letter, tolower returns the corresponding
lower-case letter. If c is not an upper-case letter,
c is returned unchanged.
int toupper (int c) ¶Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.
If c is a lower-case letter, toupper returns the corresponding
upper-case letter. Otherwise c is returned unchanged.
int toascii (int c) ¶Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.
This function converts c to a 7-bit unsigned char value
that fits into the US/UK ASCII character set, by clearing the high-order
bits. This function is a BSD extension and is also an SVID extension.
int _tolower (int c) ¶Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.
This is identical to tolower, and is provided for compatibility
with the SVID. See SVID (The System V Interface Description).
int _toupper (int c) ¶Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.
This is identical to toupper, and is provided for compatibility
with the SVID.