c primer plus第15章总结：位操作

二进制转十进制、八进制、十六进制

//二进制转十进制：
int bintodec(char* pbin)
{
    char* temp = pbin;
    int len = strlen(temp);
    int binary = 0;
    for (int i = 0; i < len; i++)
    {
        int n = temp[i] - '0';
        binary += n << (len - 1 - i);// 超过int最大值的情况未处理
    }
    return binary;
}

// 二进制转八进制：
char* bintooct(char* pbin)
{
    int bin = bintodec(pbin);
    int len = strlen(pbin);
    int temp = 0;
    char* oct;
    if (len % 3 != 0)
    {
        oct = new char[len/3 + 2];
        for (int i = len/3; i >= 0; i--, bin>>=3)
        {
            temp = (bin & 07) + '0';

            oct[i] = temp;
        }
        oct[len/3 + 1] = '\0';
    }
    else
    {
        oct = new char[len/3 + 1];
        for (int i = len/3 - 1; i >= 0; i--, bin>>=3)
        {
            temp = (bin & 07) + '0';
            oct[i] = temp;
        }
        oct[len/3] = '\0';
    }
    return oct;
}

// 二进制转十六进制，方法一：
char* bintohex(char* pbin)
{
    int bin = bintodec(pbin);
    int len = strlen(pbin);
    int temp = 0;
    char* hex;
    if (len % 4 != 0)
    {
        hex = new char[len/4 + 2];
        for (int i = len/4; i >= 0; i--, bin>>=4)
        {
            temp = (bin & 0x0F) ;
            if (temp > 9)
            {
                temp += 7 + '0';// 大于9时，将10->A..15->F;
            }
            else 
                temp += '0';
            hex[i] = temp; 
        }
        hex[len/4 + 1] = '\0';
    }
    else
    {
        hex = new char[len/4 + 1];
        for (int i = len/4 - 1; i >= 0; i--, bin>>=4)
        {
            temp = (bin & 0x0F) ;
            if (temp > 9)
            {
                temp += 7 + '0';
            }
            else 
                temp += '0';
            hex[i] = temp; 
        }
        hex[len/4] = '\0';
    }
    return hex;
}

// 二进制转十六进制，方法二：
char* int2dex(int n)
{
    char* Idex = new char[8*sizeof(int)+1];
    char* temp = NULL;
    int a = 0, b = 0;
    do
    {
        b = n % 16;
        n = n / 16;
        ++a;
        if (b <= 9)
            *Idex++ = b + '0';
        else 
            *Idex++ = b + 7 + '0';
    }while(n > 0);

    *Idex = '\0';

    temp = back(Idex - a);
  delete [] Idex;
    return temp;
}

int转二进制

char* itobs(int n)
{
    int i;
    static int size = 8 * sizeof(int);// 位 = 8*字节
    char* bins = new char[size + 1];

    for (i = size - 1; i >= 0; i--, n >>= 1)
        bins[i] = (01 & n) + '0';
    bins[size] = '\0';

    return bins;
}

flotat转二进制

void show_float(float* n)
{
    int* address = (int*)n;
    unsigned int val = *address;
    //int val = (int)*n;
    int size = 8 * sizeof(float);
    unsigned int temp = 0;
    printf("%f = ", *n);
    while (size--)
    {
        temp = val & 0x80000000;// 从高位开始判断，再左移
        val <<= 1;
        printf("%d", temp > 0 ? 1 : 0);
    }
    printf("\n");  

}

其他的关于位操作的一些blog：
http://blog.youkuaiyun.com/haoni123321/article/details/7415498
http://blog.youkuaiyun.com/dijkstar/article/details/7420515