C语言实现字符串拼接和拷贝的方法

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
 
char *str_contact(const char *,const char *);
 
char *str_contact(const char *str1,const char *str2)
{
 char *result = (char*) malloc(strlen(str1) + strlen(str2) + 1);
 if(!result)
 {
  printf("Error: malloc failed in concat! \n");
  exit(EXIT_FAILURE);
 }
 
 char *temp = result;
 while(*str1 != '\0')
 {
  *result++ = *str1++;
 }
 
 while((*result++ = *str2) != '\0')
 {
  ；
 }
 
 return temp;
}
 
 
int main(void)
{
 char *ch2 = "string_";
 char * ch3 = "_contact";
 char *result = NULL;
 result = str_contact(ch2,ch3);
 print("result = %s\n",result);
 free(result);
 result = NULL;
 return 0;
}

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
 
char *strcpy(char *dst,const char *src)
{
 assert(*dst != NULL && *src!=NULL);
 char *temp = dst;
 while(*src!='\0')
 {
 *dst++ = *src++;
 }
 *dst = '\0';
 
 return temp;
}
 
int main(void)
{
 char *ch2 = "str_cpy";
 char *ch3;
 char *result = strcpy(ch3,ch2);
 printf("result = %s\n",result);
 free(result);
 result = NULL;
 return 0;
}

#include <iostream>
#include <string>
using namespace std;
//string& operator+=(const char* str); //重载+= 操作符
//string& operator+=(const char c); //重载+= 操作符
//string& operator+=(const string& str); //重载+= 操作符
//string& append(const char* s); //把字符串s连接到当前字符串结尾
//string& append(const char* s, int n); //把字符串的前n个字符赋给当前的字符串
//string& append(const string& s); //把字符串s赋给当前字符串
//string& append(int n, char c); //用n个字符赋给当前字符串

void test01()
{
 string str1 = "我";
 str1 += "爱玩游戏";
 cout << "str1 = " << str1 << endl;
 str1 += ":";
 cout << "str1 = " << str1 << endl;

 string str2 = "LOL DNF";
 str1 += str2;
 cout << "str1 = " << str1 << endl;

 string str3 = "I";
 str3.append(" love ");
 str3.append("game abcde", 4);
 //str3.append(str2);
 cout << "str3 = " << str3 << endl;
 //lol dnf str3 = i love game
 str3.append(str2, 4, 3); //从下标4位置开始， 截取3个字符，拼接到字符串末尾
 cout << "str3 = " << str3 << endl;
}
int main()
{
 test01();
 return 0;
}