[英]Pad leading zeroes in multiples of x, using std::cout << std::hex
There are many questions regarding how to pad a fixed number of leading zeroes when using C++ streams with variables we want represented in hexadecimal format: 当使用带有我们想要的十六进制格式的变量的C ++流时,有很多关于如何填充固定数量的前导零的问题 :
std::cout << std::hex << setfill('0') << setw(8) << myByteSizedVar;
My question regards how to do this for not a fixed width, but a multiple of some fixed amount - likely 8 for the obvious reason that when comparing outputs we might want: 我的问题是如何做到这一点不是一个固定的宽度,而是一些固定数量的倍数 - 可能是8,因为明显的原因是在比较输出时我们可能需要:
0x87b003a
0xab07
To match up for width to be compared more easily (okay the top is larger - but try a bitwise comparison in your head? Easily confused.) 要比较宽度以便更容易进行比较(好吧顶部更大 - 但是尝试在头脑中进行逐位比较?容易混淆。)
0x87b003a
0x000ab07
Nice, two bytes lined up nice and neatly. 不错,两个字节排列整齐,整齐。 Except we only see 7 bits - which is not immediately obvious (especially if it were 15/16, 31/32, etc.), possibly causing us to mistake the top for a negative number (assuming signed).
除了我们只看到7位 - 这不是立即明显的(特别是如果它是15 / 16,31 / 32等),可能导致我们将顶部误认为负数(假设已签名)。
All well and good, we can set the width to 8 as above. 一切顺利,我们可以将宽度设置为8,如上所述。
However, when making the comparison next to say a 32-bit word: 但是,在进行比较时,请说一个32位字:
0x000000000000000000000000087b003a
0x238bfa700af26fa930b00b130b3b022b
It may be more unneccessary, depending on the use, or even misleading if dealing with hardware where the top number actually has no context in which to be a 32-bit word. 根据使用情况,它可能更不必要,或者如果处理硬件,其中顶部数字实际上没有上下文中的32位字,则可能更加不必要。
What I would like, is to automagically set the width of the number to be a multiple of 8, like: 我想要的是,自动将数字的宽度设置为8的倍数,如:
std::cout << std::hex << std::setfill('0') << setWidthMultiple(8) << myVar;
For results like: 对于以下结果:
0x00000000
0x388b7f62
0x0000000f388b7f62
How is this possible with standard libraries, or a minimal amount of code? 如何使用标准库或少量代码实现这一点? Without something like
Boost.Format
. 没有像
Boost.Format
这样的东西。
How about this: 这个怎么样:
template <typename Int>
struct Padme
{
static_assert(std::is_unsigned<Int>::value, "Unsigned ints only");
Int n_;
explicit Padme(Int n) : n_(n) {}
template <typename Char, typename CTraits>
friend
std::basic_ostream<Char, CTraits> & operator<<(
std::basic_ostream<Char, CTraits> & os, Padme p)
{
return os << std::setw(ComputeWidth(p.n_)) << p.n_;
}
static std::size_t ComputeWidth(Int n)
{
if (n < 0x10000) { return 4; }
if (n < 0x100000000) { return 8; }
if (n < 0x1000000000000) { return 12; }
return 16;
}
};
template <typename Int>
Padme<Int> pad(Int n) { return Padme<Int>(n); }
Usage: 用法:
std::cout << pad(129u) << "\n";
With some more work you could provide versions with different digit group sizes, different number bases etc. And for signed types you could stick std::make_unsigned
into the pad
function template. 通过一些更多的工作,您可以提供具有不同数字组大小,不同数字基础等的版本。对于签名类型,您可以将
std::make_unsigned
到pad
函数模板中。
There's no immediate support for it, because it involves more than one input value (if I understand what you're asking for correctly). 没有立即支持它,因为它涉及多个输入值(如果我理解你正确要求的话)。 The only solution which comes to mind is to use
std::max
to find the largest value, and then derive the number of digits you need from that, say by using a table: 想到的唯一解决方案是使用
std::max
来查找最大值,然后从中获取所需的位数,例如使用表:
struct DigitCount
{
unsigned long long maxValue;
int digits;
};
static const DigitCount digitCount[] =
{
{ 255UL, 2 },
{ 65535UL, 4 },
{ 16777215UL, 6 },
{ 4294967295UL, 8 },
};
and looking up the width in it. 并查看其中的宽度。
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