字符检测 cctype（ctype.h）

cctype（ctype.h）头文件用于字符检测，包括以下函数：

      字符检测类函数

      返回值：是则返回一个非0值，否返回0.

int isalnum ( int c ); 检查字符是否为字母或数字 

int isalpha ( int c ); 检查字符是否为字母 

int isblank ( int c ); 检查字符是否为空白 

int iscntrl ( int c ); 检查字符是否为控制字符 

int isdigit ( int c ); 检查字符是否为十进制数字 

int isgraph ( int c ); 检查字符是否为英文字母 

int islower ( int c ); 检查字符是否为小写字母 

int isprint ( int c ); 检查字符是否为可打印字符 

int ispunct ( int c ); 检查字符是否为标点字符 

int isspace ( int c ); 检查字符是否为一个空白 

int isupper ( int c ); 检查字符是否为大写字母字符 

int isxdigit ( int c ); 检查字符是否为十六进制数字 

字符转换类函数

int tolower( int c ); 将大写字符转换成小写字母 
int toupper ( int c ); 将小写字母装换成大写字母 
ASCII码字符检测结果表
下图为ASCII字符检测结果表格，画X的表示“是”（即真，返回值非0）
#include <iostream>#include <cctype>#include <cstdio>using namespace std;void printHead();int main(){    int choice;    char str_ch[50];    char str_ch1[50];    cout<<"input your choice,(0:大小写转换测试,1:打印ASCII字符检测结果表)\n";    cin>>choice;    if(choice == 0)    {        cout<<"input a string\n";        cin>>str_ch;        cout<<"源字符串："<<str_ch<<endl;        int len = sizeof(str_ch);        for(int i =0;i<len;i++)            str_ch1[i] = tolower(str_ch[i]);        cout<<"小写字符串："<<str_ch1<<endl;        for(int i =0;i<len;i++)            str_ch1[i] =toupper(str_ch[i]);        cout<<"大写字符串："<<str_ch1<<endl;    }    else if(choice == 1)    {        printHead();        for(int i=0;i<=127;i++)        {            printf("0x%02x%6d",i,i);            if(i>=8&&i<=13 || i==127 )            {                printf("%10s","");            }            else                printf("%10c",i);            (isalnum(i)!=0)?printf("%10s","Y"):printf("%10s","N");            (isalpha(i)!=0)?printf("%10s","Y"):printf("%10s","N");            (isblank(i)!=0)?printf("%10s","Y"):printf("%10s","N");            (iscntrl(i)!=0)?printf("%10s","Y"):printf("%10s","N");            (isdigit(i)!=0)?printf("%10s","Y"):printf("%10s","N");            (isgraph(i)!=0)?printf("%10s","Y"):printf("%10s","N");            (islower(i)!=0)?printf("%10s","Y"):printf("%10s","N");            (isprint(i)!=0)?printf("%10s","Y"):printf("%10s","N");            (ispunct(i)!=0)?printf("%10s","Y"):printf("%10s","N");            (isspace(i)!=0)?printf("%10s","Y"):printf("%10s","N");            (isupper(i)!=0)?printf("%10s","Y"):printf("%10s","N");            (isxdigit(i)!=0)?printf("%10s","Y"):printf("%10s","N");            printf("\n");        }    }    return 0;}void printHead(){    printf("%10s","value");    printf("%10s","chara");    printf("%10s","isalnum");    printf("%10s","isalpha");    printf("%10s","isblank");    printf("%10s","iscntrl");    printf("%10s","isdigit");    printf("%10s","isgraph");    printf("%10s","islower");    printf("%10s","isprint");    printf("%10s","ispunct");    printf("%10s","isspace");    printf("%10s","isupper");    printf("%10s","isxdigit");    printf("\n");}