求助:以rb+打开文件,读取到文件结尾,开始写文件,则写文件失败,不知道为什么

//返回值 0:失败 1:成功

int fill_bin_file(char *filename,unsigned char file_data,long size)

{

	FILE *fp;

	long cur_size;

	unsigned char val;

	int j;



	//============打开文件

	fp = fopen(filename,"rb+");

	if (fp == NULL)

	{

		printf("open file fail\n");

		return 0;

	}

	//==========获取文件的当前长度

	if (fseek(fp,0,SEEK_END)!=0)

	{

		printf("seek file fail\n");

		fclose(fp);

		return 0;

	}

	cur_size = ftell(fp);

	//==========校验文件长度

	if ((cur_size == -1)||(cur_size+32 >= size))

	{

		printf("get file size fail\n");

		fclose(fp);

		return 0;

	}

	printf("file current size is : %u\n",cur_size);

	//=========计算从文件开始到当前位置的异或校验

	crc_val = 0;

	j=0;

	if (fseek(fp,0,SEEK_SET)!=0)

	{

		printf("seek file fail\n");

		fclose(fp);

		return 0;

	}

	while(j<cur_size)

	{

		if (fread(&val,1,1,fp)!=1)

		{

			printf("read file error\n");

			fclose(fp);

			return 0;

		}

		crc_val ^= val;

		j++;

	}

	//===========填充文件

	while (cur_size < size-32)

	{

		if(fwrite(&file_data,1,1,fp)!=1)

		{

			printf("write file fail\n");

			fclose(fp);

			return 0;

		}

		cur_size++;

		crc_val ^= file_data;

	}

	//==========填写后缀信息

	//填写程序名

	for (j=0;j<10;j++)

	{

		fwrite(&dev_type[j],1,1,fp);

		cur_size++;

		crc_val ^= dev_type[j];

	}

	//填写版本

	for (j=0;j<10;j++)

	{

		fwrite(&version[j],1,1,fp);

		cur_size++;

		crc_val ^= version[j];

	}

	//填写保留

	for (j=0;j<11;j++)

	{

		fwrite(&file_data,1,1,fp);

		cur_size++;

		crc_val ^= file_data;

	}

	//填写校验

	fwrite(&crc_val,1,1,fp);

	fclose(fp);

	return 1;

}