c语言isalnum()函数的用法介绍判断字符是否为英文或数字，c语言函数汇总有哪些？isalnum()函数要引入什么头文件？返回值是什么？

isalnum()头文件：#include <ctype.h>

定义函数：int isalnum(int c);

isalnum()函数说明：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)。

附加说明：此为宏定义，非真正函数。

isalnum()应用实例源码：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]);
}

函数实例执行结果：
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