C isalnum()

isalnum() 函数定义为：

int isalnum(int argument);

它定义在 ctype.h 头文件中。

isalnum() 参数

• argument - 一个字符

isalnum()返回值

• 如果 argument 是字母数字字符，则返回 1。
• 如果 argument 既不是字母也不是数字，则返回 0。

示例 #1: isalnum() 函数返回值

#include <stdio.h>
#include <ctype.h>
int main()
{
    char c;
    int result;

    c = '5';
    result = isalnum(c);
    printf("When %c is passed, return value is %d\n", c, result);

    c = 'Q';
    result = isalnum(c);
    printf("When %c is passed, return value is %d\n", c, result);

    c = 'l';
    result = isalnum(c);
    printf("When %c is passed, return value is %d\n", c, result);

    c = '+';
    result = isalnum(c);
    printf("When %c is passed, return value is %d\n", c, result);

    return 0;
}

输出

When 5 is passed, return value is 1
When Q is passed, return value is 1
When l is passed, return value is 1
When + is passed, return value is 0

示例 #2: 检查字符是否是字母数字字符

#include <stdio.h>
#include <ctype.h>
int main()
{
    char c;
    printf("Enter a character: ");
    scanf("%c", &c);

    if (isalnum(c) == 0)
        printf("%c is not an alphanumeric character.", c);
    else
        printf("%c is an alphanumeric character.", c);
    
    return 0;
}

输出

Enter a character: 0
0 is an alphanumeric character.