我的函数 READ() 似乎工作正常，除了当我转储输入时我得到的比我要求的多。既不是 0 也不是 1 的奇怪字符。我打赌这是由于我的指针使用(取消引用运算符)，但我似乎无法弄清楚它在做什么。使其输出正确数据的任何帮助都会有所帮助。此外，一些解释为什么它的错误用法，以及一些关于如何不再这样做的好技巧。谢谢，你们是最棒的。
在 MSVC++ 2010 Express 下编译:
#include <iostream>
using namespace std;
struct Holder
{
unsigned char *bits; // holds our bits
unsigned char header[6]; // Always 6 bits
unsigned char hasid[1]; // Always 1 bit
unsigned char cid[4]; // always 4 bits
};
// Turns our Bytes Into Bits
// Credit: Ben Voigt(http://stackoverflow.com)
void BIT(const char *bytes, size_t len, char *bitStr)
{
while (len--) {
bitStr[0] = (*bytes & 0x80) ? '1': '0';
bitStr[1] = (*bytes & 0x40) ? '1': '0';
bitStr[2] = (*bytes & 0x20) ? '1': '0';
bitStr[3] = (*bytes & 0x10) ? '1': '0';
bitStr[4] = (*bytes & 0x08) ? '1': '0';
bitStr[5] = (*bytes & 0x04) ? '1': '0';
bitStr[6] = (*bytes & 0x02) ? '1': '0';
bitStr[7] = (*bytes & 0x01) ? '1': '0';
bitStr += 8;
bytes++;
}
*bitStr = 0;
}
// This function is not working correctly
void READ( unsigned char *BITS, unsigned char *PACKET_ID, unsigned char *HAS_CHANNEL_ID, unsigned char *CHANNEL_ID, unsigned char *PACKET)
{
//=====================================================
// The Below Header Info Is Always The Same
//=====================================================
// Packet ID ALWAYS 6 BITS
PACKET_ID[0] = BITS[2];
PACKET_ID[1] = BITS[3];
PACKET_ID[2] = BITS[4];
PACKET_ID[3] = BITS[5];
PACKET_ID[4] = BITS[6];
PACKET_ID[5] = BITS[7];
// Packet Has Channel ID (1==true) ALWAYS 1 BIT
HAS_CHANNEL_ID[0] = BITS[1];
// Channel ID ALWAYS 4 BIT
CHANNEL_ID[0] = BITS[0];
CHANNEL_ID[1] = BITS[15];
CHANNEL_ID[2] = BITS[14];
CHANNEL_ID[3] = BITS[13];
//=====================================================
// The above Header Info Is Always The Same
//=====================================================
//Variables For Looping
int P = 16; // This is the start of all data, always
int B = 24; // Every 24 bits, the loop goes into an IF_STATMENT and reads backwards into the array, then continues normally
int A = 1; // This Increases every 24 bits
int Z = 0; // This holds how many times we loop. Used for IF_STATMENT formula
int I = 0; // This gets zeroed out every IF_STATMENT and keeps our loop int i in sync
PACKET[0] = BITS[12];
PACKET[1] = BITS[11];
PACKET[2] = BITS[10];
PACKET[3] = BITS[9];
PACKET[4] = BITS[8];
// Starts our main loop...
for(int i=5 ; i < sizeof(BITS) ; i++, P++, Z++)
{
PACKET[i] = BITS[P];
if( (A * B) == Z) // A==1 B==24 Z==FOR_LOOP
{
I = 0; // ZERO THIS OUT. THIS IS USED FOR P COUNTER
A++; // Increase by one for IF_STATMENT formula
if( (P+7) <= sizeof(BITS)) // if P+7 is less then or equal to BITS then its okay todo the following
{ // which is needed because maybe P+7 is bigger then BITS, so this wouldnt be good ...
PACKET[i] = BITS[P+7];
I++;
}
if( (P+6) <= sizeof(BITS)) // Explained Above
{
PACKET[i+1] = BITS[P+6];
I++;
}
if( (P+5) <= sizeof(BITS)) // Explained Above
{
PACKET[i+2] = BITS[P+5];
I++;
}
if( (P+4) <= sizeof(BITS)) // Explained Above
{
PACKET[i+3] = BITS[P+4];
I++;
}
if( (P+3) <= sizeof(BITS)) // Explained Above
{
PACKET[i+4] = BITS[P+3];
I++;
}
if( (P+2) <= sizeof(BITS)) // Explained Above
{
PACKET[i+5] = BITS[i+2];
I++;
}
if( (P+1) <= sizeof(BITS)) // Explained Above
{
PACKET[i+6] = BITS[P+1];
I++;
}
if( P <= sizeof(BITS)) // Explained Above
{
PACKET[i+7] = BITS[P];
I++;
}
P += I; // We have been increasing I each time we do one of the statments to keep track of how many loops
if(I != 0) // we need to add to P to keep it on track ... + I-1 to keep i on track
i += I-1;
}
}
}
int main()
{
const char p40[] =
{
0x81, 0x11, 0xb6, 0x1e, 0xc9, 0x67, 0x0e, 0x52, 0x0b, 0xec, 0xff, 0x3b, 0xa8, 0xfa, 0x2a, 0x62,
0x41, 0x79, 0xd2, 0x75, 0x7b, 0x93, 0xaf, 0xb4, 0xcf, 0x10, 0x3a, 0x12, 0x4d, 0x4b, 0x60, 0x64,
0xcc, 0x78, 0x01, 0xd1, 0x83, 0xbc, 0x27
};
Holder k; // Call our struct for holding stuff
unsigned char bitbit[sizeof(p40)*8]; // bitbit is an array that is p40 * 8 to get the amount of bits being made using BIT function
BIT(p40,sizeof(p40),(char*)bitbit); // BIT takes p40, and turns it into bits and stores them in bitbit
k.bits = bitbit; // now k.bits is equal to bitbit
cout << k.bits; // dumps k.bits to screen
cout << "\n"; // space to see ...
unsigned char r[sizeof(k.bits-11)]; // r is k.bits - 11 because 11 bits are used for something else
READ(k.bits, k.header,k.hasid, k.cid,r); //This puts k.bits into READ function. Itll store the info into the struct
cout << "\nPACKET_HEADER:\n";
cout << k.header; // This dump seems to be displaying more then what its suppose too...
cout << "\nHAS_CANNEL:\n";
cout << k.hasid; // This dump seems to be displaying more then what its suppose too...
cout << "\nCHANNEL_ID:\n";
cout << k.cid; // This dump seems to be displaying more then what its suppose too...
cout << "\nPACKET_BITS:\n";
cout << r; // The last dump (r) is displaying all inputs into the function READ + r.
int a; // Used to hang program ...
cin >> a;
return 0;
}
最佳答案
您将数据保存在 char 数组中，因此当您将它们传递给 std::cout 时，运算符假定以 null 结尾的 C 字符串。除非您的 header 保证以 null 结尾，否则 std::cout 将超出数组的末尾并打印出比您希望的更多的内容。
一种解决此问题的 hacky 方法:
struct Holder
{
unsigned char *bits; // holds our bits
unsigned char header[6]; // Always 6 bits
unsigned char header_term = '\0' // null terminator
unsigned char hasid[1]; // Always 1 bit
unsigned char hasid_term = '\0' // null terminator
unsigned char cid[4]; // always 4 bits
unsigned char cid_term = '\0' // null terminator
};
假设您的编译器没有对 Holder 中的字段重新排序，这应该会导致 std::cout 仅打印您期望的字节数。
这只回答了您问题的一部分。我现在正在发帖，如果我弄清楚其余部分，我会进行编辑。
ETA:查看 READ，您的问题似乎又是缺少空终止。您需要数组中的一个额外字符来保存空字符('\0'，几乎普遍等于 NULL，它本身几乎总是 0)这将告诉 std::cout C 字符串正在结束.此外，这是一种向 Holder 提供空终止的更简洁的方法:
struct Holder
{
unsigned char *bits; // holds our bits
unsigned char header[7]={0,0,0,0,0,0,'\0'}; // Always 6 bits
unsigned char hasid[2]={0,'\0'}; // Always 1 bit
unsigned char cid[5]={0,0,0,0,'\0'}; // always 4 bits
};
我保留了上面原始的、丑陋的修复程序，因为它说明了导致您的代码打印额外垃圾的规则。
关于C++ BitStreaming 解码函数返回不良值(指针问题？)，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/7671142/