C/C++的各种骚操作

1.C风格字符串头指针p复制到q中

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while(*q++ = *p++);

2.while循环趋近于0的写法🐶

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while(n --> 0) {
	// 实际上也就是 -- >
}

3.数组下标

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int arr[] = {1,2,3,4,5,6};
for(int i = 0; i < 6; i++) {
	cout << arr[i] << endl;
	//cout << i[arr] << endl;
	//以上两种写法等价
}

4.两种高段位判断是否为回文数

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int isRev_1(int i) {
    int rev = 0;
    int tmp = i;

    while (tmp) {
        rev *= 10;
        rev += tmp % 10;
        tmp /= 10;
    }

    return rev == i;
}

int isRev_2(int i) {
    #define REV_TBL_SIZE 5
    static int tbl[][REV_TBL_SIZE] = {
        {1000000001, 100000010, 10000100, 1001000, 110000},
        { 100000001,  10000010,  1000100,  101000,  10000},
        {  10000001,   1000010,   100100,   11000,      0},
        {   1000001,    100010,    10100,    1000,      0},
        {    100001,     10010,     1100,       0,      0},
        {     10001,      1010,      100,       0,      0},
        {      1001,       110,        0,       0,      0},
        {       101,        10,        0,       0,      0},
        {        11,         0,        0,       0,      0},
        {         1,         0,        0,       0,      0},
        {         0,         0,        0,       0,      0},
    };

    if (i < 0) {
        i = -i;
    }

    int *tbl_p = (int *) tbl;
    while (i < *tbl_p) {
        tbl_p += REV_TBL_SIZE;
    }

    int tbi, mask;
    for (
        tbi = 0;
        tbi < REV_TBL_SIZE && (mask = tbl_p[tbi]);
        ++tbi
    ) {
        if (mask != 1000000001 && i >= 5 * mask) {
            i -= 5 * mask;
        }
        if (i >= 2 * mask) {
            i -= 2 * mask;
        }
        if (i >= mask) {
            i -= mask;
        }
        if (i >= mask) {
            i -= mask;
        }
        if (i & ((1 << tbi) - 1)) {
            return 0;
        }
    }

    return !i;
}

5.错误兼容抖机灵

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#define ture true 
#define mian main
#define return reutrn
#define viod void

6.快速乘

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// x * y % p
long long multiply(long long x,long long y,long long p)
{
	long long ret = 0;
	for( ; y; y >>= 1)
	{
		if(y & 1)ret = (ret + x) % p;
		x = (x + x) % p;
	}
	return ret;
}

7.abs的高段位写法

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int abs1(int x) {
	int s[] = {-x,x}
	return s[x > 0];
}

int abs2(int x) {
	return (x ^ (x >> 31)) - (x >> 31);	
}

8.类型转换编译期检查

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#define STATIC_CHECK(expr, msg) \
{\
    class ERROR_##msg {} ;\
    (void) sizeof((CompileTimeChecker<(expr) != 0> (ERROR_##msg())));\
}
template <bool> struct CompileTimeChecker {
    CompileTimeChecker(...);
};
template<> struct CompileTimeChecker<false> { };

template <typename To, typename From>
To safe_reinterpret_cast(From from) {
    STATIC_CHECK(sizeof(To) >= sizeof(From), Destination_Too_Narrow);
    return reinterpret_cast<To>(from);
}
  1. Pointer Traits
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class NullType;
struct EmptyType {};

template <typename T>
class TypeTraits {
private:
    template <typename U> struct PointerTraits {
        enum { result = false };
        using PointeeType = NullType;
    };
    template <typename U> struct PointerTraits<U*> {
        enum { result = true };
        using PointeeType = U;  
    };
    
    template <typename U> struct PToMTraits {
        enum { result = false };  
    };
    template <typename U, typename V> 
    struct PToMTraits<U V::*> {
        enum { result = true };
    }
public:
    enum { isPointer = PointerTraits<T>::result };
    using PointeeType = PointerTraits<T>::PointeeType;
  
    enum { isMenmberPointer = PToMTraits<T>::result };
};
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