---
name: "isupper"
section: "3"
platform: "macos"
package: "Libc"
version: "1752.120.2"
release: "macOS 26.5"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/isupper"
---

# isupper(3)

upper-case character test

## NAME

**isupper** – upper-case character test

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

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

*int*\

**isupper**(*int c*);

## DESCRIPTION

The **isupper**() function tests for any upper-case letter. The value of the argument must be representable as an *unsigned char* or the value of EOF.

In the ASCII character set, this includes the following characters (preceded by their numeric values, in octal):

| |
| --- |
| 101 \`\`A'' 102 \`\`B'' 103 \`\`C'' 104 \`\`D'' 105 \`\`E'' |
| 106 \`\`F'' 107 \`\`G'' 110 \`\`H'' 111 \`\`I'' 112 \`\`J'' |
| 113 \`\`K'' 114 \`\`L'' 115 \`\`M'' 116 \`\`N'' 117 \`\`O'' |
| 120 \`\`P'' 121 \`\`Q'' 122 \`\`R'' 123 \`\`S'' 124 \`\`T'' |
| 125 \`\`U'' 126 \`\`V'' 127 \`\`W'' 130 \`\`X'' 131 \`\`Y'' |
| 132 \`\`Z'' |

## RETURN VALUES

The **isupper**() function returns zero if the character tests false and returns non-zero if the character tests true.

## 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 **iswupper**() function should be used instead.

## SEE ALSO

[ctype(3)](/ctype/3.md), [isalnum\_l(3)](/isalnum_l/3.md), [iswupper(3)](/iswupper/3.md), [toupper(3)](/toupper/3.md), [ascii(7)](/ascii/7.md)

## STANDARDS

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