strncat函数

  

   

    

     

    
    

     

      /*
     
    
   

    

     

    
    

     

      原型：extern char *strncat(char *dest,char *src,int n);
     
    
   

    

     

    
    

     

      用法：#include <string.h>
     
    
   

    

     

    
    

     

      功能：把src所指字符串的前n个字符添加到dest结尾处（覆盖dest结尾处的'\0'）并添加'\0'。
     
    
   

    

     

    
    

     

      说明：src和dest所指内存区域不可以重叠且dest必须有足够的空间来容纳src的字符串。
     
    
   

    

     

    
    

     

      返回指向dest的指针。
     
    
   

    

     

    
    

     

      */
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      #include <stdio.h>
     
    
   

    

     

    
    

     

      #include <string.h>
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      char *
     
    
   

    

     

    
    

     

      strncat(char *dst, const char *src, size_t n)
     
    
   

    

     

    
    

     

      {
     
    
   

    

     

    
    

     
  if (n != 0)
     
    
   

    

     

    
    

     

        {
     
    
   

    

     

    
    

     
 //保存两个操作字符串的首地址
     
    
   

    

     

    
    

     
 char *d = dst;
     
    
   

    

     

    
    

     
 const char *s = src;
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 //将指向dst的指针d移到字符串末尾,指向'\0'
     
    
   

    

     

    
    

     
 while (*d != 0)
     
    
   

    

     

    
    

     

       d++; 
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 //复制过程
     
    
   

    

     

    
    

     
 do {
     
    
   

    

     

    
    

     
 //如果到达了src字符串的末尾,则复制终止
     
    
   

    

     

    
    

     
 if ((*d = *s++) == 0)
     
    
   

    

     

    
    

     
 break;
     
    
   

    

     

    
    

     
 //移向下一个元素
     
    
   

    

     

    
    

     

       d++;
     
    
   

    

     

    
    

     

       } while (--n != 0); //复制后剩余要复制的元素个数
     
    
   

    

     

    
    

     

       *d = 0; //复制完毕后,将最后一个元素置为'\0'
     
    
   

    

     

    
    

     

        }
     
    
   

    

     

    
    

     
  return dst; 
     
    
   

    

     

    
    

     

      }
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      int main() 
     
    
   

    

     

    
    

     

      {
     
    
   

    

     

    
    

     
 char str[50] = "Hello ";
     
    
   

    

     

    
    

     
 char str2[50] = "World!";
     
    
   

    

     

    
    

     
 strcat(str, str2);
     
    
   

    

     

    
    

     
 strncat(str, " Goodbye World!", 3);
     
    
   

    

     

    
    

     
 puts(str);
     
    
   

    

     

    
    

     

      }
     
    
  
 

//linux源码

  

   

    

     

    
    

     

      #ifndef __HAVE_ARCH_STRNCAT 
     
    
   

    

     

    
    

     

      /** 
     
    
   

    

     

    
    

     

       * strncat - Append a length-limited, %NUL-terminated string to another 
     
    
   

    

     

    
    

     

       * @dest: The string to be appended to 
     
    
   

    

     

    
    

     

       * @src: The string to append to it 
     
    
   

    

     

    
    

     

       * @count: The maximum numbers of bytes to copy 
     
    
   

    

     

    
    

     

       * 
     
    
   

    

     

    
    

     

       * Note that in contrast to strncpy(), strncat() ensures the result is 
     
    
   

    

     

    
    

     

       * terminated. 
     
    
   

    

     

    
    

     

       */  
     
    
   

    

     

    
    

     

      char *strncat(char *dest, const char *src, size_t count) 
     
    
   

    

     

    
    

     

      {  
     
    
   

    

     

    
    

     
 char *tmp = dest;  
     
    
   

    

     

    
    

     
  
     
    
   

    

     

    
    

     
 if (count) {  
     
    
   

    

     

    
    

     
 while (*dest)  
     
    
   

    

     

    
    

     

       dest++;  
     
    
   

    

     

    
    

     
 while ((*dest++ = *src++) != 0) {  
     
    
   

    

     

    
    

     
 if (--count == 0) {  
     
    
   

    

     

    
    

     

       *dest = '\0';  
     
    
   

    

     

    
    

     
 break;  
     
    
   

    

     

    
    

     

       }  
     
    
   

    

     

    
    

     

       }  
     
    
   

    

     

    
    

     

       }  
     
    
   

    

     

    
    

     
 return tmp;  
     
    
   

    

     

    
    

     

      }  
     
    
   

    

     

    
    

     

      EXPORT_SYMBOL(strncat);  
     
    
   

    

     

    
    

     

      #endif 
     
    
  
 

//标准C源码

  

   

    

     

    
    

     

      /***
     
    
   

    

     

    
    

     

      *strncat.c - append n chars of string to new string
     
    
   

    

     

    
    

     

      *
     
    
   

    

     

    
    

     

      * Copyright (c) 1985-1997, Microsoft Corporation. All rights reserved.
     
    
   

    

     

    
    

     

      *
     
    
   

    

     

    
    

     

      *Purpose:
     
    
   

    

     

    
    

     

      * defines strncat() - appends n characters of string onto
     
    
   

    

     

    
    

     

      * end of other string
     
    
   

    

     

    
    

     

      *
     
    
   

    

     

    
    

     

      *******************************************************************************/
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      #include <cruntime.h>
     
    
   

    

     

    
    

     

      #include <string.h>
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      /***
     
    
   

    

     

    
    

     

      *char *strncat(front, back, count) - append count chars of back onto front
     
    
   

    

     

    
    

     

      *
     
    
   

    

     

    
    

     

      *Purpose:
     
    
   

    

     

    
    

     

      * Appends at most count characters of the string back onto the
     
    
   

    

     

    
    

     

      * end of front, and ALWAYS terminates with a null character.
     
    
   

    

     

    
    

     

      * If count is greater than the length of back, the length of back
     
    
   

    

     

    
    

     

      * is used instead. (Unlike strncpy, this routine does not pad out
     
    
   

    

     

    
    

     

      * to count characters).
     
    
   

    

     

    
    

     

      *
     
    
   

    

     

    
    

     

      *Entry:
     
    
   

    

     

    
    

     

      * char *front - string to append onto
     
    
   

    

     

    
    

     

      * char *back - string to append
     
    
   

    

     

    
    

     

      * unsigned count - count of max characters to append
     
    
   

    

     

    
    

     

      *
     
    
   

    

     

    
    

     

      *Exit:
     
    
   

    

     

    
    

     

      * returns a pointer to string appended onto (front).
     
    
   

    

     

    
    

     

      *
     
    
   

    

     

    
    

     

      *Uses:
     
    
   

    

     

    
    

     

      *
     
    
   

    

     

    
    

     

      *Exceptions:
     
    
   

    

     

    
    

     

      *
     
    
   

    

     

    
    

     

      *******************************************************************************/
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      char * __cdecl strncat (
     
    
   

    

     

    
    

     

       char * front,
     
    
   

    

     

    
    

     

       const char * back,
     
    
   

    

     

    
    

     

       size_t count
     
    
   

    

     

    
    

     

       )
     
    
   

    

     

    
    

     

      {
     
    
   

    

     

    
    

     
 char *start = front;
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 while (*front++)
     
    
   

    

     

    
    

     

       ;
     
    
   

    

     

    
    

     

       front--;
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 while (count--)
     
    
   

    

     

    
    

     
 if (!(*front++ = *back++))
     
    
   

    

     

    
    

     
 return(start);
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

       *front = '\0';
     
    
   

    

     

    
    

     
 return(start);
     
    
   

    

     

    
    

     

      }
     
    
  
 

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原文链接：blog.csdn.net/qq523176585/article/details/11949895