C语言专题——标准库<ctype.h>

1 字符测试函数

1> 函数原型均为int isxxxx(int)
2> 参数为int, 任何实参均被提升成整型
3> 只能正确处理处于[0, 127]之间的值

isalpha 'A'~'Z', 'a'~'z'
isdigit '0'~'9'
isxdigit '0'~'9', 'A'~'F', 'a'~'f'
isalnum isalpha || isdigit

islower 'a'~'z'
isupper 'A'~'Z'

isspace
9 '\t' (tab: 水平制表位)
10 '\n' (line feed: 换行)
11 '\v' (home: 垂直制表位)
12 '\f' (form feed: 换页)
13 '\r' (carriage return: 回车)
32 ' ' (space: 空格)

isgraph 33~126
isprint isgraph || ' '
ispunct isgraph && !isalnum

iscntrl 0~31, 127

2 字符映射函数

1> 函数原型为int toxxxx(int)
2> 对参数进行检测, 若符合范围则转换, 否则不变

int tolower(int); 'A'~'Z' ==> 'a'~'z'
int toupper(int); 'a'~'z' ==> 'A'~'Z'

3 附测试代码

#include <stdio.h>
#include <ctype.h>

char (* isxx_name[]) =
{
"isalpha",
"isdigit",
"isxdigit",
"isalnum",

"islower",
"isupper",

"isspace",

"isgraph",
"isprint",
"ispunct",

"iscntrl"
};

int (* isxx_list[])(int) =
{
isalpha,
isdigit,
isxdigit,
isalnum,

islower,
isupper,

isspace,

isgraph,
isprint,
ispunct,

iscntrl
};

int main()
{
int i, k;

for (i=0; i<sizeof(isxx_list)/sizeof(isxx_list[0]); i++)
{
printf("Testing %s\n", isxx_name[i]);
for (k=0; k<128; k++)
if (isxx_list[i](k))
printf("%3d %c\n", k, k);
printf("\n");
}

return 0;
}

source: 《C & C++ Code Capsules》