C语言isalnum()函数：判断字符是否为英文字母或数字
头文件：
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1
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#include <ctype.h>
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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：
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1
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int isalnum(int c);
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【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。
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#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]);
}
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输出结果：
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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
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C语言isalpha()函数：判断字符是否为英文字母
头文件：
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1
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#include <ctype.h>
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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：
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1
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int isalpha(int c);
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【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。
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1
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8
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#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 character\n", str[i]);
}
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执行结果：
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2
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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
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