---
name: "toupper"
section: "3"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/toupper"
---

# toupper(3)

lower case to upper case letter conversion

## NAME

**toupper**, **toupper\_l** – lower case to upper case letter conversion

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<ctype.h\>**

*int*\

**toupper**(*int c*);

*int*\

**toupper\_l**(*int c*, *locale\_t loc*);

## DESCRIPTION

The **toupper**() and **toupper\_l**() functions convert a lower-case letter to the corresponding upper-case letter. The argument must be representable as an *unsigned char* or the value of EOF.

The **toupper\_l**() function takes an explicit locale argument, whereas the **toupper**() function uses the current global or per-thread locale.

## RETURN VALUES

If the argument is a lower-case letter, the **toupper**() and **toupper\_l**() functions return the corresponding upper-case letter if there is one; otherwise, the argument is returned unchanged.

## COMPATIBILITY

The 4.4BSD extension of accepting arguments outside of the range of the *unsigned char* type in locales with large character sets is considered obsolete and may not be supported in future releases. The **towupper**() or **towupper\_l**() function should be used instead.

## SEE ALSO

[ctype(3)](/ctype/3.md), [ctype\_l(3)](/ctype_l/3.md), [isupper(3)](/isupper/3.md), [isupper\_l(3)](/isupper_l/3.md), [towupper(3)](/towupper/3.md), [towupper\_l(3)](/towupper_l/3.md), [xlocale(3)](/xlocale/3.md)

## STANDARDS

The **toupper**() function conforms to ISO/IEC 9899:1990 (“ISO C90”).