check_sum.c

此为计算机网络课程设计C/C++源代码 包括一些协议的底层实现

/*
计算校验和
*/

#include <stdio.h>
#include <stdlib.h>

void main(int argc,char *argv[])
{
	FILE *fp;
	char ch;
	unsigned char chrl,chrh;
	unsigned int count=0,checksum=0,chr=0;
	unsigned long int sum=0;

	//打开文件argv[1]
	if ( (fp = fopen(argv[1],"r") )==NULL )
	{
		printf("\n\n File can't be opened");
		exit(1);
	}
	printf("\n\nthe type of output:data---sum\n\n");

	//从文本文件中读取字符，并进行数据处理
	while (1)
	{
		if ( (ch = fgetc(fp)) != EOF )
		{
			count++;
			if ( ch != ' ' )
			{
				if (count%12==0)
				{
					printf("\n");
				}

				//将字符转换为相应整型变量
				if (ch>='0' && ch<='9')
				{
					ch-='0';
				}
				else if (ch>='a' && ch<='f')
				{
					ch=ch-'a'+10;
				}
				else if (ch>='A' && ch<='F')
				{
					ch=ch-'A'+10;
				}

				/*计算8字节数的累加值，将奇数位累加到长整型sum的15-8位，偶数位累加到低8-0位*/
				/*这样就避免了数据个数为奇偶的处理操作*/
				if (count%2==1)
				{
					chrh=ch<<4;
				}
				else
				{
					chrl=ch & 0x0f;
					chr=chrh | chrl;
					if (count%4==2)
					{
						sum+=chr<<8;
					}
					else if (count%4==0)
					{
						sum+=chr;
					}
					printf("%x--%lx    ",chr,sum);
				}
			}
			else
			{
				count--;
			}
		}
		else
		{
			break;
		}
	}

	//将sum由32位折合成16位
	if (sum>>16)
	{
		checksum=( (long)(sum>>16)+(long)(sum&0x0000ffff) );
	}
	checksum=checksum&0x0000ffff;

	//结果输出
	printf("\n\nsum:%lx---checksum:%x",sum,checksum);
	printf("\n\nsource:argc=%d,\targv=%s\n",argc,argv[1]);

	fclose(fp);
}