strncpy函數(shù)實現(xiàn)及簡單應(yīng)用

ID:51090 · 發(fā)表于 2014-9-24 22:30

//:Vc++6.0  String  strncpy函數(shù)
//功能：指定大小的字符串拷貝
//參數(shù)：dest 目標(biāo)字符串  str 要考的字符串  num 拷貝大小
//返回值：dest字符串地址
#include<stdio.h>

char *strncpy(char *dest, const char *str, int num);

int main()
{
char str1[]= "To be or not to be";
char str2[6];
strncpy (str2,str1,5);
printf("str2 = %s\n", str2);

return 0;
}

char *strncpy(char * dest, const char *str, int num)
{
//查錯
if (dest == NULL || str == NULL)
{
perror("dest or str");
return NULL;
}
//求長度
char *temp1 = dest;
const char *temp2 = str;
int len;
while (*(temp2++) != '\0');
len = temp2 - str;

//拷貝
if (num <= 0)
      *temp1 = '\0';
else  if (num >= len)
{
      while (*str != '\0')
         *(temp1++) = *(str++);
      *temp1 = '\0';
}
else
{
int i;
      for (i = 0; i < num; i++)
      {
         *(temp1++) = *(str++);
      }
      *temp1 = '\0';
}
return dest;
}
//在vc++6.0中的運行結(jié)果為：str2 = To be
//注：在拷貝時已經(jīng)在尾部加了'\0'//:~

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