定义：

int isalnum (int c)

表头文件：

#include<ctype.h>

说明：

检查参数c是否为英文字母或阿拉伯数字, 在标准c中相当于使用"isalpha(c) || isdigit(c)"做测试。

返回值：

若参数c为字母或数字, 则返回TRUE, 否则返回NULL(0)。

相关函数：

isalpha, isdigit, islower, isupper

附加说明：

此为宏定义, 非真正函数。

示例：

/* 找出str 字符串中为英文字母或数字的字符*/
#include < ctype.h>
main()
{
	char str[]=”123c@#FDsP[e?”;
	int i;
	for (i=0;str[i]!=0;i++ )
		if ( isalnum(str[i])) printf(“%c is an alphanumeric character\n”,str[i]);
}

执行：

1 is an apphabetic character
2 is an apphabetic character
3 is an apphabetic character
c is an apphabetic character
F is an apphabetic character
D is an apphabetic character
s is an apphabetic character
P is an apphabetic character
e is an apphabetic character