C语言isalnum()函数：判断字符是否为英文字母或数字

头文件：

#include <ctype.h>

isalnum() 用来判断一个字符是否为英文字母或数字，相当于 isalpha(c) || isdigit(c)，其原型为：

int isalnum(int c);

【参数】c 为需要检测的字符。

【返回值】若参数c 为字母或数字，若 c 为 0 ~ 9 a ~ z A ~ Z 则返回非 0，否则返回 0。

注意，isalnum()为宏定义，非真正函数。

【实例】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 charactern", str[i]); }

输出结果：

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

C语言isalpha()函数：判断字符是否为英文字母

头文件：

#include <ctype.h>

isalpha() 用来判断一个字符是否是英文字母，相当于 isupper(c)||islower(c)，其原型为：

int isalpha(int c);

【参数】c 为需要被检测的字符。

【返回值】若参数c 为英文字母（a ~ z A ~ Z），则返回非 0 值，否则返回 0。

注意，isalpha() 为宏定义，非真正函数。

【实例】找出str 字符串中为英文字母的字符。

#include <ctype.h> main(){ char str[] = "123c@#FDsP[e"; int i; for (i = 0; str[i] != 0; i++) if(isalpha(str[i])) printf("%c is an alphanumeric charactern", str[i]); }

执行结果：

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