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Location: /reference/cctype/isalnum/
HTTP/1.1 200 OK
Server: nginx
Date: Tue, 29 Jul 2025 09:36:28 GMT
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Checks whether c is either a decimal digit or an uppercase or lowercase letter.
The result is true if either isalpha or isdigit would also return true.
Notice that what is considered a letter may depend on the locale being used; In the default "C" locale, what constitutes a letter is what returns true by either isupper or islower.
For a detailed chart on what the different ctype functions return for each character of the standard ANSII character set, see the reference for the <cctype> header.
In C++, a locale-specific template version of this function (isalnum) exists in header <locale>.
Output:
Reference
C library:
- <cassert> (assert.h)
- <cctype> (ctype.h)
- <cerrno> (errno.h)
-
<cfenv> (fenv.h)C++11
- <cfloat> (float.h)
-
<cinttypes> (inttypes.h)C++11
- <ciso646> (iso646.h)
- <climits> (limits.h)
- <clocale> (locale.h)
- <cmath> (math.h)
- <csetjmp> (setjmp.h)
- <csignal> (signal.h)
- <cstdarg> (stdarg.h)
-
<cstdbool> (stdbool.h)C++11
- <cstddef> (stddef.h)
-
<cstdint> (stdint.h)C++11
- <cstdio> (stdio.h)
- <cstdlib> (stdlib.h)
- <cstring> (string.h)
-
<ctgmath> (tgmath.h)C++11
- <ctime> (time.h)
-
<cuchar> (uchar.h)C++11
- <cwchar> (wchar.h)
- <cwctype> (wctype.h)
Containers:
-
<array>C++11
- <deque>
-
<forward_list>C++11
- <list>
- <map>
- <queue>
- <set>
- <stack>
-
<unordered_map>C++11
-
<unordered_set>C++11
- <vector>
-
Input/Output:
Multi-threading:
-
<atomic>C++11
-
<condition_variable>C++11
-
<future>C++11
-
<mutex>C++11
-
<thread>C++11
-
Other:
- <algorithm>
- <bitset>
-
<chrono>C++11
-
<codecvt>C++11
- <complex>
- <exception>
- <functional>
-
<initializer_list>C++11
- <iterator>
- <limits>
- <locale>
- <memory>
- <new>
- <numeric>
-
<random>C++11
-
<ratio>C++11
-
<regex>C++11
- <stdexcept>
- <string>
-
<system_error>C++11
-
<tuple>C++11
-
<type_traits>C++11
-
<typeindex>C++11
- <typeinfo>
- <utility>
- <valarray>
function
<cctype>
isalnum
int isalnum ( int c );
Check if character is alphanumeric
The result is true if either isalpha or isdigit would also return true.
Notice that what is considered a letter may depend on the locale being used; In the default "C" locale, what constitutes a letter is what returns true by either isupper or islower.
For a detailed chart on what the different ctype functions return for each character of the standard ANSII character set, see the reference for the <cctype> header.
In C++, a locale-specific template version of this function (isalnum) exists in header <locale>.
Parameters
- c
- Character to be checked, casted as an int, or EOF.
Return Value
A value different from zero (i.e., true) if indeed c is either a digit or a letter. Zero (i.e., false) otherwise.Example
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Output:
The first 4 characters are alphanumeric. |
See also
- isalpha
- Check if character is alphabetic (function)
- isdigit
- Check if character is decimal digit (function)
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Spotted an error? contact us