C语言字符串操作函数实现

1、字符串反转 – strRev

void strRev(char *str)
{
    assert(NULL != str);

    int length=strlen(str);
    char *end=str+length-1;

    while(end > str)
    {
        *str=(*str)^(*end);
        *end=(*str)^(*end);
        *str=(*str)^(*end);

        end--;
        str++;
    }
}

2、字符串复制 – strcpy

char *strcpy(char *strDest, const char *strStr)
{
    assert((NULL != strDest) && (NULL != strStr));

    char *Dest=strDest;

    while((*Dest++)=(*strStr++))
    {}

    return strDest;
}

3、字符串拼接 –strcat

char *strcat(char *strDest, const char *strStr)
{
    assert((NULL != strDest) && (NULL != strStr));

    int length=strlen(strDest);

    char *Dest=strDest+length;

    while((*Dest++)=(*strStr++))
    {}

    return strDest;
}

4、字符串比较 –strcmp

int strcmp(const char *strDest, const char *strStr)
{
    assert((NULL != strDest) && (NULL != strStr));

    while(0==(*strDest - *strStr) && *strDest )
    {
        strDest++;
        strStr++;
    }

    if(*strDest > *strStr)
        return 1;
    else if(*strDest < *strStr)
        return -1;
    else
        return 0;
}

5、字符串长度 –strlen

int strlen(const char *strStr)
{
    assert(NULL != strStr);

    int length = 0;

    while('' != *strStr)
    {
        length++;
        strStr++;
    }

    return length;
}

6、字符串转数字 –atoi

int atoi(const char *strStr)
{
    assert(NULL != strStr);

    int minus = 0;
    int begin = 0;
    int sum = 0;

    while('' !=*strStr)
    {
        if(0==begin && (isdigit(*strStr) || '+'==*strStr || '-'==*strStr))
        {
            begin = 1;

            if('-'==*strStr)
            {
                minus = 1;
                strStr++;
                continue;
            }
        }
        else if(!isdigit(*strStr))
        {
            printf("format is wrong !
");
            exit(1);
        }

        if(1==begin)
        {
            sum = sum*10 + (*strStr-'0');
        }

        strStr++;
    }

    return minus ? (-sum):(sum);
}

7、数字转字符串 –atoi

char *itoa(int num)
{
    int temp,i,j;
    char array[10];
    static char strDest[10];

    for(temp = num,i=0; i<10 && temp ;i++)
    {
        array[i]=temp%10+'0';
        temp/=10;
    }


    for(i=i-1,j=0 ; i>=0 && j<10; i--,j++)
    {
        strDest[j]=array[i];
    }
    strDest[j]='';

    return strDest;
}

8、计算字符串中元音字符的个数

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

int isVowel(char letter)
{
    switch(toupper(letter))
    {
        case 'A':
        case 'E':
        case 'I':
        case 'O':
        case 'U':
            return 1;
        default:
            return 0;
    }
}

int countVowel(const char * strStr)
{
    assert(NULL != strStr);

    int count=0;

    while('' !=*strStr++)
    {
        if(isVowel(*strStr))
            count++;
    }

    return count;
}

int main()
{
    char a[10]="hwlulr";

    printf("%d
",countVowel(a));

    return 0;
}

9、判断一个字符串是否是回文

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<assert.h>
#include<ctype.h>

int isEqual(char a,char b)
{
    if(a==b)
        return 1;

    return 0;
}

int isPalindrome(const char * strStr)
{
    assert(NULL != strStr);

    int length=strlen(strStr);
    int i,j;

    for(i=0,j=length-1; i<j ; i++,j--)
    {
        /*跳过空格和符号*/
        while(' '== *(strStr+i) || !isalpha(*(strStr+i)))
            i++;
        while(' '== *(strStr+j) || !isalpha(*(strStr+j)))
            j--;

        if(0==isEqual(*(strStr+i),*(strStr+j)))
            return 0;
    }

    return 1;
}

int main()
{
    char a[10]="heo o, e h";

    printf("%s
",isPalindrome(a) ? "is Palindrome" : "is not Palindrome");

    return 0;
}