---
name: "toupper"
section: "3avr"
platform: "linux"
package: "avr-libc"
version: "1:2.2.1-1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/ctype/3avr"
---

# toupper(3avr)

\<ctype.h\>: Character Operations

Part of [ctype(3avr)](/ctype/3avr.md).

## NAME

ctype - \<ctype.h\>: Character Operations

## SYNOPSIS

### Character classification routines

These functions perform character classification. They return true or false status depending whether the character passed to the function falls into the function's classification (i.e. **isdigit()** returns true if its argument is any value '0' though '9', inclusive). If the input is not an unsigned char value, all of this function return false.  int **isalnum** (int \_\_c)\
 int **isalpha** (int \_\_c)\
 int **isascii** (int \_\_c)\
 int **isblank** (int \_\_c)\
 int **iscntrl** (int \_\_c)\
 int **isdigit** (int \_\_c)\
 int **isgraph** (int \_\_c)\
 int **islower** (int \_\_c)\
 int **isprint** (int \_\_c)\
 int **ispunct** (int \_\_c)\
 int **isspace** (int \_\_c)\
 int **isupper** (int \_\_c)\
 int **isxdigit** (int \_\_c)\

### Character convertion routines

This realization permits all possible values of integer argument. The **toascii()** function clears all highest bits. The **tolower()** and **toupper()** functions return an input argument as is, if it is not an unsigned char value.  int **toascii** (int \_\_c)\
 int **tolower** (int \_\_c)\
 int **toupper** (int \_\_c)\

## Detailed Description

These functions perform various operations on characters.

```
#include <ctype.h>
```

## Function Documentation

### int isalnum (int \_\_c)` [extern]`

Checks for an alphanumeric character. It is equivalent to `(isalpha(c) || isdigit(c))`.

### int isalpha (int \_\_c)` [extern]`

Checks for an alphabetic character. It is equivalent to `(isupper(c) || islower(c))`.

### int isascii (int \_\_c)` [extern]`

Checks whether `c` is a 7-bit unsigned char value that fits into the ASCII character set.

### int isblank (int \_\_c)` [extern]`

Checks for a blank character, that is, a space or a tab.

### int iscntrl (int \_\_c)` [extern]`

Checks for a control character.

### int isdigit (int \_\_c)` [extern]`

Checks for a digit (0 through 9).

### int isgraph (int \_\_c)` [extern]`

Checks for any printable character except space.

### int islower (int \_\_c)` [extern]`

Checks for a lower-case character.

### int isprint (int \_\_c)` [extern]`

Checks for any printable character including space.

### int ispunct (int \_\_c)` [extern]`

Checks for any printable character which is not a space or an alphanumeric character.

### int isspace (int \_\_c)` [extern]`

Checks for white-space characters. For the AVR-LibC library, these are: space, form-feed ('\\f'), newline ('\\n'), carriage return ('\\r'), horizontal tab ('\\t'), and vertical tab ('\\v').

### int isupper (int \_\_c)` [extern]`

Checks for an uppercase letter.

### int isxdigit (int \_\_c)` [extern]`

Checks for a hexadecimal digits, i.e. one of 0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F.

### int toascii (int \_\_c)` [extern]`

Converts `c` to a 7-bit unsigned char value that fits into the ASCII character set, by clearing the high-order bits.

**Warning**

Many people will be unhappy if you use this function. This function will convert accented letters into random characters.

### int tolower (int \_\_c)` [extern]`

Converts the letter `c` to lower case, if possible.

### int toupper (int \_\_c)` [extern]`

Converts the letter `c` to upper case, if possible.

## Author

Generated automatically by Doxygen for AVR-LibC from the source code.