我正在使用格式化的输出，如
0 6.0303 16.052 40.523 100 40.557 16.167 6.7314 1.8967 0
0 4.5593 13.16 25.342 41.927 25.354 13.312 4.9988 1.9527 0
0 3.0952 6.6864 13.531 17.01 13.544 6.7291 3.466 0.91553 0
0 1.1353 3.466 5.0842 7.3242 5.0842 3.4981 1.2207 0.56076 0
0 0.54474 0.95825 2.153 2.1179 2.153 0.95825 0.5928 0.10681 0
0 0.085449 0.38452 0.45166 0.78392 0.45166 0.38452 0.085449 0.048065 0
0 0.032043 0.042725 0.15221 0.11444 0.15221 0.042725 0.032043 0 0
0 0 0 0 0 0 0 0 0 0
目标是准备一张桌子。然而，该表如下所示：
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如果小数点后的第一个数字为零，则显示的长度为一个字符。我怎么能避免它？
答案 0 :(得分：1)
使用：
std::cout << std::fixed;
默认行为是在＆＃34; precision＆＃34;中显示数字位数。 std :: fixed将显示精确的位数。因此，默认情况下，您将显示5个有效数字。固定时，5个数字 例如：
auto a = 2017.0;
default = 2017
fixed = 2017.00000
auto b = 1e-10;
default= 1e-10
fixed = 0.00000
答案 1 :(得分：0)
嗯。所以我想在考虑所有边缘情况后这样做。我确定我没有处理好一些权利，而且我认为这在C中会更干净，但我认为它没问题（如果方式过于设计）。
如果你知道发生了什么，请随意编辑评论。）。
除了一些警告：
这是过度设计和未经测试的方式。
不便携，但可以通过更多的工作来实现。
我在你的输入中添加了一行额外的测试/角落案例。
这可能比您需要的更多，但您可以概括一下。或者使用能够做得更好的库。
#include <cmath>
#include <cstdint>
#include <iomanip>
#include <iostream>
#include <vector>
const std::vector<std::vector<double>> array = {
// OP's data.
{0, 6.0303, 16.052, 40.523, 100, 40.557, 16.167, 6.7314, 1.8967, 0},
{0, 4.5593, 13.16, 25.342, 41.927, 25.354, 13.312, 4.9988, 1.9527, 0},
{0, 3.0952, 6.6864, 13.531, 17.01, 13.544, 6.7291, 3.466, 0.91553, 0},
{0, 1.1353, 3.466, 5.0842, 7.3242, 5.0842, 3.4981, 1.2207, 0.56076, 0},
{0, 0.54474, 0.95825, 2.153, 2.1179, 2.153, 0.95825, 0.5928, 0.10681, 0},
{0, 0.085449, 0.38452, 0.45166, 0.78392, 0.45166, 0.38452, 0.085449, 0.048065, 0},
{0, 0.032043, 0.042725, 0.15221, 0.11444, 0.15221, 0.042725, 0.032043, 0, 0},
{0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
// My test data.
{1e-7, 1.12031e-34, 1e-34, 1e-6, 1e33, 1e-8, 1.3123233e93, 1e32, 1.e99, 1.e100},
{-1e-7, -1.12031e-34, -1e-34, -1e-6, -1e33, -1e-8, -1.3123233e93, -1e32, -1.e99, -1.09e100},
};
// Warning: any widths under 7 cannot accurately print the double -1e+100...
// (or many like it). There's just no way to express that any more tersely!
constexpr uint8_t kWidth = 7;
// Most of these are really obvious but help make the code slightly cleaner.
// "."
constexpr uint8_t kWidthTakenByDecimalSeparator = 1;
// "-"
constexpr uint8_t kWidthTakenByNegativeSign = 1;
// "e+" or "e-"
constexpr uint8_t kWidthOfExtraScientificNotationCharacters = 2;
// On *MY* system, 1.0e-08 is always printed, not 1.0e-8. This basically handles
// the leading 0 on the exponent. Tune accordingly (or find the right compiler
// flags that give you the right number(s).
constexpr uint8_t kMinimumWidthOfScientificNotationExponent = 2;
int main() {
// Store the original std::cout flags.
auto old_flags = std::cout.flags();
for (auto& row : array) {
for (auto& value : row) {
const double log10_value = log10(std::abs(value));
const uint8_t available_width = kWidth - (value < 0) * kWidthTakenByNegativeSign;
// Handle numbers greater than 10^kWidth or less than 10^-kWidth in
// scientific notation.
const bool use_scientific_notation =
value != 0 &&
(log10_value < -1.0 * available_width + kWidthTakenByDecimalSeparator +
kWidthTakenByNegativeSign ||
log10_value > available_width);
std::cout << ' ' << std::setw(kWidth);
if (use_scientific_notation) {
const double log10log10_value = log10(log10_value);
const uint8_t num_digits_in_exponent_of_scientific_notation =
std::max(kMinimumWidthOfScientificNotationExponent,
static_cast<uint8_t>(log10log10_value ));
const uint8_t num_digits_desired_after_decimal_scientific =
std::max(1.0, log10log10_value);
uint8_t potential_new_precision =
available_width - num_digits_in_exponent_of_scientific_notation -
kMinimumWidthOfScientificNotationExponent -
kWidthTakenByDecimalSeparator -
num_digits_desired_after_decimal_scientific;
// Lazy underflow checking. Needed?
if (potential_new_precision > available_width) {
potential_new_precision = 0;
}
std::cout << std::scientific
<< std::setprecision(potential_new_precision);
} else {
// We take the max with 1.0 to compensate for the leading 0 in decimals.
// If your system doesn't put a leading zero there, remove it.
const uint8_t number_of_digits_before_decimal_fixed =
std::max(log10_value + 1.0, 1.0);
const uint8_t number_of_digits_desired_after_decimal_fixed =
available_width - kWidthTakenByDecimalSeparator -
number_of_digits_before_decimal_fixed;
// Fixed width decimals -- this means that the code
// std::cout << std::precision(n)
// tells the stream to use n digits *after the decimal*.
std::cout << std::fixed
<< std::setprecision(
number_of_digits_desired_after_decimal_fixed);
}
std::cout << value;
}
std::cout << '\n';
}
// Reset the flags to their old value, and flush the output buffer.
std::cout.flush();
std::cout.flags(old_flags);
}
有趣的东西：
示例输出，kWidth = 7：
0.00000 6.03030 16.0520 40.5230 100.000 40.5570 16.1670 6.73140 1.89670 0.00000
0.00000 4.55930 13.1600 25.3420 41.9270 25.3540 13.3120 4.99880 1.95270 0.00000
0.00000 3.09520 6.68640 13.5310 17.0100 13.5440 6.72910 3.46600 0.91553 0.00000
0.00000 1.13530 3.46600 5.08420 7.32420 5.08420 3.49810 1.22070 0.56076 0.00000
0.00000 0.54474 0.95825 2.15300 2.11790 2.15300 0.95825 0.59280 0.10681 0.00000
0.00000 0.08545 0.38452 0.45166 0.78392 0.45166 0.38452 0.08545 0.04806 0.00000
0.00000 0.03204 0.04272 0.15221 0.11444 0.15221 0.04272 0.03204 0.00000 0.00000
0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000
1.0e-07 1.1e-34 1.0e-34 1.0e-06 1.0e+33 1.0e-08 1.3e+93 1.0e+32 1.0e+99 1e+100
-1e-07 -1e-34 -1e-34 -1e-06 -1e+33 -1e-08 -1e+93 -1e+32 -1e+99 -1e+100
示例输出，kWidth = 10：
0.00000000 6.03030000 16.0520000 40.5230000 100.000000 40.5570000 16.1670000 6.73140000 1.89670000 0.00000000
0.00000000 4.55930000 13.1600000 25.3420000 41.9270000 25.3540000 13.3120000 4.99880000 1.95270000 0.00000000
0.00000000 3.09520000 6.68640000 13.5310000 17.0100000 13.5440000 6.72910000 3.46600000 0.91553000 0.00000000
0.00000000 1.13530000 3.46600000 5.08420000 7.32420000 5.08420000 3.49810000 1.22070000 0.56076000 0.00000000
0.00000000 0.54474000 0.95825000 2.15300000 2.11790000 2.15300000 0.95825000 0.59280000 0.10681000 0.00000000
0.00000000 0.08544900 0.38452000 0.45166000 0.78392000 0.45166000 0.38452000 0.08544900 0.04806500 0.00000000
0.00000000 0.03204300 0.04272500 0.15221000 0.11444000 0.15221000 0.04272500 0.03204300 0.00000000 0.00000000
0.00000000 0.00000000 0.00000000 0.00000000 0.00000000 0.00000000 0.00000000 0.00000000 0.00000000 0.00000000
0.00000010 1.1203e-34 1.0000e-34 0.00000100 1.0000e+33 0.00000001 1.3123e+93 1.0000e+32 1.0000e+99 1.000e+100
-0.0000001 -1.120e-34 -1.000e-34 -0.0000010 -1.000e+33 -1.000e-08 -1.312e+93 -1.000e+32 -1.000e+99 -1.09e+100
这比我想象的要多。