isalnum

int isalnum ( int c );

• Checks whether c is either a decimal digit or an uppercase or lowercase letter.
• 检查给定的字符是否为当前 C 本地环境所分类的字母数字字符。在默认本地环境中，下列字符为字母数字：
  • 数字（ 0123456789 ）
  • 大写字母（ ABCDEFGHIJKLMNOPQRSTUVWXYZ ）
  • 小写字母（ abcdefghijklmnopqrstuvwxyz ）
    若 c 的值不能表示为 unsigned char 且不等于 EOF ，则行为未定义。

Parameters

c

• Character to be checked, casted as an int, or EOF.
• c - 要分类的字符

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.
• 若字符为字母数字字符，则为非零，否则为 0 。

Example

//
// Created by zhangrongxiang on 2018/1/31 13:33
// File isalnum
//#include <stdio.h>
#include <ctype.h>
#include <locale.h>/*isalnum*/int main(void) {///unsigned char c = '\xdf'; // ISO-8859-1 中的德文字母 ßprintf("isalnum('\\xdf') in default C locale returned %d\n", c, !!isalnum(c));if (setlocale(LC_CTYPE, "de_DE.iso88591"))printf("isalnum('\\xdf') in ISO-8859-1 locale returned %d\n", !!isalnum(c));if (setlocale(LC_CTYPE, "en_US.UTF-8"))//isalnum('\xdf') in UTF-8 locale returned 0printf("isalnum('\\xdf') in UTF-8 locale returned %d\n", !!isalnum(c));///int var1 = 'd';int var2 = '2';int var3 = '\t';int var4 = ' ';if (isalnum(var1)) {printf("var1 = |%c| 是字母数字\n", var1);} else {printf("var1 = |%c| 不是字母数字\n", var1);}if (isalnum(var2)) {printf("var2 = |%c| 是字母数字\n", var2);} else {printf("var2 = |%c| 不是字母数字\n", var2);}if (isalnum(var3)) {printf("var3 = |%c| 是字母数字\n", var3);} else {printf("var3 = |%c| 不是字母数字\n", var3);}if (isalnum(var4)) {printf("var4 = |%c| 是字母数字\n", var4);} else {printf("var4 = |%c| 不是字母数字\n", var4);}
//  var1 = |d| 是字母数字
//  var2 = |2| 是字母数字
//  var3 = |    | 不是字母数字
//  var4 = | | 不是字母数字///int i;char str[] = "c3po...";i = 0;while (isalnum(str[i])) i++;//The first 4 characters are alphanumeric.printf("The first %d characters are alphanumeric.\n", i);return 0;}

文章参考

• http://zh.cppreference.com/w/c/string/byte/isalnum
• http://www.cplusplus.com/reference/cctype/isalnum/
• http://www.runoob.com/cprogramming/c-function-isalnum.html