strcat()的编写

1、strcat()

#include <windows.h>

#include <assert.h>

#include <iostream>

//strcat()函数分4部分写

//1.定义4个char*

//2.变量检查不为空assert()

//3.指针指向第一个字符串的末尾

//4.逐个字符的赋值

char *strcat(char  *strDest, char *strSrc)

{

    char *address = strDest;

    assert( (strDest != NULL)&&(strSrc != NULL));

    while(*strDest)

    {

        strDest++;

    }

    while(*strDest++ = *strSrc++)

    {

        ;

    }

    return address;

}

void main()

{

    char l[] ="li";    //注意此处需要时开辟空间的数组

    char *w = "wen";

    strcat(l,w);

    std::cout<<l;

}

2、strcpy()

#define  NULL 0

#include <assert.h>

#include <stdlib.h>

#include <iostream>

char * strcpy(char *strDest, char *strSrc)

{

    char *address = strDest;

    assert(strDest!=NULL&&strSrc!=NULL);

    while (*strDest++ =  *strSrc++)

    {

        ;

    }

    return address;

}

void main()

{

    char a[] = "li";

    char *b="lwn";

    strcpy(a,b);

    std::cout<<a;

    system("pause");

}

3、strcmp()

#include <stdlib.h>

#include <iostream>

int strcmp(const char *strDest, const char *strSrc)

{

    while (*strDest == *strSrc)

    {

        if (*strDest =='\0')        //注意时单引号

            return ;

        strDest++;

        strSrc++;

    }

    return *strDest - *strSrc;

}

void main()

{

    char a[] = "li";

    char *b="li";

    strcmp(a,b);

    std::cout<<strcmp(a,b);

    system("pause");

}

4.strlen()　　//由于strlen()函数不加头文件也能调用下文将名字改为strln()

#include <iostream>

int strln(const char *strDest)

{

    int i=;

    while (*strDest !='\0')

    {

        strDest++;i++;

    }

    return i;

}

void main()

{

    char a[] = "li4";

    std::cout<<strln(a);

    system("pause");

}