字符串处理函数的模拟实现（strlen、strstr、strcat、strcmp、strcpy、memmove、memcpy）

1.strlen()函数的模拟实现（计数器法）#define _CRT_SECURE_NO_WARNINGS 1#include <stdio.h>#include <stdlib.h>#include <assert.h>int my_strlen(const char *arr){    int count=0;    assert(arr!=NULL);    while(*arr!='\0')    {        arr++;        count++;    }    return count;}int main(){    char arr[]="abcdgddf";    int ret;    ret=my_strlen(arr);    printf("%d\n",ret);    system("pause");    return 0;}strlen()函数的模拟实现（指针）#define _CRT_SECURE_NO_WARNINGS 1#include <stdio.h>#include <stdlib.h>#include <assert.h>int my_strlen(char *arr){    char *p=arr;    assert(arr!=NULL);    while(*p!='\0')    {        p++;    }    return p-arr;}int main(){    char arr[]="sfjfkdsjk";    int ret=0;    ret=my_strlen(arr);    printf("%d\n",ret);    system("pause");    return 0;}strlen()函数的模拟实现（递归）#define _CRT_SECURE_NO_WARNINGS 1#include <stdio.h>#include <stdlib.h>#include <assert.h>int my_strlen(const char *arr){    assert(arr!=NULL);    if(*arr=='\0')    {        return 0;    }    else    {        return 1+my_strlen(arr+1);    }}int main(){    char arr[]="sfjfkdsjk";    int ret=0;    ret=my_strlen(arr);    printf("%d\n",ret);    system("pause");    return 0;}2.strstr()函数的模拟实现#define _CRT_SECURE_NO_WARNINGS 1#include <stdio.h>#include <stdlib.h>#include <assert.h>char *my_strstr(char *dest,char *src){    assert(dest!=NULL);    assert(src!=NULL);    while(*dest!='\0')    {        char *p=dest;        char *q=src;        char *start=NULL;        if(*p==*q)        {            start=p;            while(*p==*q)            {                p++;                q++;            }            if(*q=='\0')            {                return start;            }        }        dest++;    }    return 0;}int main(){    char arr1[]="abbcdef";    char arr2[]="bcde";    char *ret=my_strstr(arr1,arr2);    if(ret==0)    {        printf("没找到\n");    }    else    {        printf("%s\n",ret);    }    system("pause");    return 0;}3.strcpy()函数的模拟实现#define _CRT_SECURE_NO_WARNINGS 1#include <stdio.h>#include <stdlib.h>#include <assert.h>char *my_strcpy(char *dest,const char *src){    char *ret=dest;    assert(dest!=NULL);    assert(src!=NULL);    while(*src!='\0')    {        *dest=*src;        dest++;        src++;    }    return ret;}int main(){    char arr1[]="lkjhefg";    char arr2[]="abcd";    char *ret=my_strcpy(arr1,arr2);    printf("%s\n",ret);    system("pause");    return 0;}4.strncpy()函数的模拟实现#define _CRT_SECURE_NO_WARNINGS 1#include <stdio.h>#include <stdlib.h>#include <assert.h>char *my_strncpy(char *dest,char *src,int n){    char *ret=dest;    assert(dest!=NULL);    assert(src!=NULL);    while(n!=0 && *src!='\0')    {        *dest++=*src++;        n--;    }    if(n!=0)    {        while(n)        {            *dest='\0';            n--;        }    }    return ret;}int main(){    char arr1[]="kpouycdefgh";    char arr2[]="abcdefghi";    char *ret=my_strncpy(arr1,arr2,12);    printf("%s\n",ret);    system("pause");    return 0;}5.strcat()函数的模拟实现#define _CRT_SECURE_NO_WARNINGS 1#include <stdio.h>#include <stdlib.h>#include <assert.h>#include <string.h>char *my_strcat(char *dest,char *src){    char *ret=dest;    char *p=dest+strlen(dest);    assert(dest!=NULL);    assert(src!=NULL);    while(*src!='\0')    {        *p++=*src++;    }    return ret;}int main(){    char arr1[20]="abc";    char arr2[10]="defg";    char *ret=my_strcat(arr1,arr2);    printf("%s\n",ret);    system("pause");    return 0;}6.strncat()函数的模拟实现#define _CRT_SECURE_NO_WARNINGS 1#include <stdio.h>#include <stdlib.h>#include <assert.h>#include <string.h>char *my_strncat(char *dest,char *src,int n){    char *ret=dest;    char *p=dest+strlen(dest);    assert(dest!=NULL);    assert(src!=NULL);    while(n && *src!='\0')    {        *p++=*src++;        n--;    }    if(n!=0)    {        while(n)        {            *p='\0';            n--;        }    }    return ret;}int main(){    char arr1[20]="abc";    char arr2[10]="defg";    char *ret=my_strncat(arr1,arr2,5);    printf("%s\n",ret);    system("pause");    return 0;}7.strcmp()函数的模拟实现#define _CRT_SECURE_NO_WARNINGS 1#include <stdio.h>#include <stdlib.h>#include <assert.h>int my_strcmp(char *dest,char *src){    assert(dest!=NULL);    assert(src!=NULL);    while(*dest==*src)    {        if(*dest=='\0')        {            return 0;        }        dest++;        src++;    }    return *dest-*src;}int main(){    char arr1[]="abcdefgsgr";    char arr2[]="abcdef";    int ret=my_strcmp(arr1,arr2);    printf("%d\n",ret);    system("pause");    return 0;}8.strncmp()函数的模拟实现#define _CRT_SECURE_NO_WARNINGS 1#include <stdio.h>#include <stdlib.h>#include <assert.h>int my_strncmp(char *dest,char *src,int n){    assert(dest!=NULL);    assert(src!=NULL);    while(n &&*dest==*src)    {        /*if(*dest=='\0')        {            return 0;        }*/        dest++;        src++;        n--;    }    return *dest-*src;}int main(){    char arr1[]="abcdefrtgdger";    char arr2[]="abcrtdg";    int ret=my_strncmp(arr1,arr2,2);    printf("%d\n",ret);    system("pause");    return 0;}9.memcpy()函数的模拟实现#define _CRT_SECURE_NO_WARNINGS 1#include <stdio.h>#include <stdlib.h>#include <assert.h>void *my_memcpy(void *dest,void *src,int n){    void *ret=dest;    assert(dest!=NULL);    assert(src!=NULL);    while(n)    {        *(char *)dest=*(char *)src;        dest=(char *)dest+1;        src=(char *)src+1;        n--;    }    return ret;}int main(){    char arr1[20]="dfskfkljsffds";    char arr2[]="saf .v/?";    char *ret=my_memcpy(arr1,arr2,7);    printf("%s\n",ret);    system("pause");    return 0;}10.memmove()函数的模拟实现#define _CRT_SECURE_NO_WARNINGS 1#include <stdio.h>#include <stdlib.h>#include <assert.h>void *my_memmove(void *dest,void *src,size_t count){    void *ret=dest;    assert(dest!=NULL);    assert(src!=NULL);    if(dest>src && (char *)dest<(char *)src+count )    {            while(count--)        {            *((char *)dest+count)=*((char *)src+count);        }    }    else    {        while(count--)        {            *(char *)dest=*(char *)src;            dest=(char *)dest+1;            src=(char *)src+1;        }    }    return ret;}int main(){    int arr[]={1,2,3,4,5,6,7,8,9,0};    int i=0;    int sz=sizeof(arr)/sizeof(arr[0]);    my_memmove(arr+4,arr,4*sizeof(int));    for(i=0;i<sz;i++)    {        printf("%d ",arr[i]);    }    system("pause");    return 0;}