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

# isalpha(3)

alphabetic character test

## NAME

**isalpha** – alphabetic character test

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

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

*int*\

**isalpha**(*int c*);

## DESCRIPTION

The **isalpha**() function tests for any character for which [isupper(3)](/isupper/3.md) or [islower(3)](/islower/3.md) is true. 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'' 141 \`\`a'' 142 \`\`b'' 143 \`\`c'' 144 \`\`d'' |
| 145 \`\`e'' 146 \`\`f'' 147 \`\`g'' 150 \`\`h'' 151 \`\`i'' |
| 152 \`\`j'' 153 \`\`k'' 154 \`\`l'' 155 \`\`m'' 156 \`\`n'' |
| 157 \`\`o'' 160 \`\`p'' 161 \`\`q'' 162 \`\`r'' 163 \`\`s'' |
| 164 \`\`t'' 165 \`\`u'' 166 \`\`v'' 167 \`\`w'' 170 \`\`x'' |
| 171 \`\`y'' 172 \`\`z'' |

## RETURN VALUES

The **isalpha**() 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 **iswalpha**() function should be used instead.

## SEE ALSO

[ctype(3)](/ctype/3.md), [isalnum\_l(3)](/isalnum_l/3.md), [islower(3)](/islower/3.md), [isupper(3)](/isupper/3.md), [iswalpha(3)](/iswalpha/3.md), [ascii(7)](/ascii/7.md)

## STANDARDS

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