代码我正确为什么我得到'++'需要l值 [英] code i correct why am i getting '++' needs l-value

问题描述

当我在Visaul Studio中编译此代码时，我得到了以下代码，这是一个a.cpp文件:我收到一个错误:-

错误C2105:'++'在行
 sum = sum + *(((word16 *)addr)++ ;; 
 



我该怎么办才能消除错误



 #include   ><   stdio.h  > //printf()需要
 #include   <   stdlib.h  > //rand()需要

//  -----类型定义----------------- ----------------------------------------- 
 typedef   unsigned   char 字节； // 字节是一个字符
 typedef   unsigned   short  //  16位字是一个简短的整数
 typedef   unsigned   int  word32; //  32位字是整数

//  -----定义------------------ --------------------------------------------- 
#define BUFFER_LEN 6//缓冲区长度
 // 外部字符数据[6]； 
字符 data [ 6 ] = "  CM00";
//  -----原型------------------ ------------------------------------------ 
word16校验和(字符 * addr，word32计数)；

//  =====主程序================= ======================================
 int  tarun( void )
{
  //  byte buff [BUFFER_LEN]; //数据包字节的缓冲区

  word16检查； //  16位校验和值
  word32我； // 循环计数器

  // 具有BUFFER_LEN随机字节的加载缓冲区
   for (i =  0 ; i< BUFFER_LEN; i ++)
  {
    //  buff [i] =(字节)rand(); 
data [i] =(byte)rand();
  }

  // 计算16位校验和
  //  check = checksum(buff，BUFFER_LEN); 
  校验=校验和(数据，BUFFER_LEN);

  // 输出校验和
  printf(" ，选中)；
  
}

//  ========================= ================================================== === 
//  =计算从位置addr开始的计数字节的Internet校验和= 
//  ========================= ================================================== === 
word16校验和(字符 * addr，word32计数)
{
  注册 word32 sum =  0 ;

  // 主求和循环
  同时(计数>  1 )
  {
    sum = sum + *(((word16 *)addr)++++;
    count = count- 2 ;
  }

  // 添加剩余字节(如果有)
  如果(计数>  0 )
    sum = sum + *(((byte *)addr);

  // 将32位总和折叠为16位
   while (总和>>> 16)
    sum =(sum& 0xFFFF)+(sum>>  16 );

  返回(〜sum);
} 
 
解决方案
 
表达式"sum + *((word16 *)addr)"不是左值，即您无法为其分配值.我认为您需要将增量作为单独的语句进行.
 
 
这取决于您要增量的值.

如果要增加addr指向的word16，则... 



(*((word16 *)addr))++; 



...应该这样做.



知道了这一点后，我不确定您要做什么，将addr转换为word16指针看起来有点错误.
 
 
再看一下您的代码，我可以说您不应修改addr指向的数据，因为它是恒定数据.



  char 数据[ 6 ] =   CM00"; 
 



数据指向常量.



  const   char  data [ 6 ] = " ; 
 



会是正确的.
 
 
I have the following code its an a.cpp file when i compile this code in visaul studio i am getting an error :-

error C2105: '++' needs l-value
 at the line  
sum = sum + *((word16 *) addr)++;




What should i do to remove the error



#include <stdio.h>                  // Needed for printf()
#include <stdlib.h>                 // Needed for rand()

//----- Type defines ----------------------------------------------------------
typedef unsigned char      byte;    // Byte is a char
typedef unsigned short int word16;  // 16-bit word is a short int
typedef unsigned int       word32;  // 32-bit word is an int

//----- Defines ---------------------------------------------------------------
#define BUFFER_LEN        6      // Length of buffer
//extern char data[6];
char data[6]="CM00";
//----- Prototypes ------------------------------------------------------------
word16 checksum(char *addr, word32 count);

//===== Main program ==========================================================
int tarun(void)
{
  //byte        buff[BUFFER_LEN]; // Buffer of packet bytes

  word16      check;            // 16-bit checksum value
  word32      i;                // Loop counter

  // Load buffer with BUFFER_LEN random bytes
  for (i=0; i<BUFFER_LEN; i++)
  {
    //buff[i] = (byte) rand();
	data[i]=(byte) rand();
  }

  // Compute the 16-bit checksum
  //check = checksum(buff, BUFFER_LEN);
  check = checksum(data, BUFFER_LEN);

  // Output the checksum
  printf("checksum = %04X \n", check);
  
}

//=============================================================================
//=  Compute Internet Checksum for count bytes beginning at location addr     =
//=============================================================================
word16 checksum(char *addr, word32 count)
{
  register word32 sum = 0;

  // Main summing loop
  while(count > 1)
  {
    sum = sum + *((word16 *) addr)++;
    count = count - 2;
  }

  // Add left-over byte, if any
  if (count > 0)
    sum = sum + *((byte *) addr);

  // Fold 32-bit sum to 16 bits
  while (sum>>16)
    sum = (sum & 0xFFFF) + (sum >> 16);

  return(~sum);
}
解决方案
the expression "sum + *((word16 *) addr)" is not an lvalue i.e. you cannot assign to it. I think you will need to do the increment as a seperate statement.

That will depend on what value you want to increment.

If you want to increment the word16 that addr is pointing to, then ...



(*((word16 *) addr))++;



... should do it.



Having sead that, I am not sure what you are trying to do, casting addr to a word16 pointer looks a bit wrong.

Having looked at your code a bit more I can say that you should not modify the data that addr is pointing to because it is constant data.



char data[6]="CM00";




data points to constant.



const char data[6]="CM00";




Would be correct.


                        
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