[英]Limit number of trailing zeroes for fixed output
我需要一些使用C ++流进行输出格式化的帮助。 我想打印一个固定的小数点,最多2个尾随数字。 我尝试了以下方法:
#include <iostream>
#include <iomanip>
using namespace std;
int main(int argc, char **argv)
{
float testme[] = { 0.12345, 1.2345, 12.345, 123.45, 1234.5, 12345 };
std::cout << std::setprecision(2) << std::fixed;
for(int i = 0; i < 6; ++i)
{
std::cout << testme[i] << std::endl;
}
return 0;
}
输出为:
0.12
1.23
12.35
123.45
1234.50
12345.00
但我想有
0.12
1.23
12.35
123.45
1234.5
12345
是否可以在不使用其他字符串操作的情况下实现这一目标?
我不知道合适的操纵器,因此您可以使用:
#include <iostream>
#include <iomanip>
#include <cmath>
template <typename T>
struct Fixed
{
const T& value;
const unsigned precision;
const T significant;
Fixed(const T& value, unsigned precision)
: value(value), precision(precision), significant(std::pow(10, precision))
{}
void write(std::ostream& stream) const {
// Adjust stream settings
std::ostream::char_type restore_fill = stream.fill('0');
std::ios_base::fmtflags restore_flags = stream.setf(
std::ios_base::fixed, std::ios_base::floatfield);
std::streamsize restore_precision = stream.precision(0);
// Split the floating point into an integral and rounded fractional part
T integral;
unsigned long fractional = std::round(significant * std::modf(value, &integral));
// Determine the length of the fractional part
unsigned digits = precision;
while(fractional && fractional % 10 == 0) {
fractional /= 10;
--digits;
}
// Carry over to the integral part
if( ! digits && fractional) {
integral += 1;
fractional = 0;
}
// Output
stream << integral;
if(fractional) {
stream << '.' << std::setw(digits) << fractional;
}
// Restore stream settings
stream.precision(restore_precision);
stream.flags(restore_flags);
stream.fill(restore_fill);
}
};
template <typename T>
inline Fixed<T> fixed(const T& value, unsigned precision) {
return Fixed<T>(value, precision);
}
template <typename T>
inline std::ostream& operator << (std::ostream& stream, const Fixed<T>& value) {
value.write(stream);
return stream;
}
int main(int argc, char **argv)
{
float testme[] = { 0.12345, 1.2345, 12.345, 123.45, 1234.5, 12345 };
for(int i = 0; i < 6; ++i)
{
std::cout << fixed(testme[i], 2) << std::endl;
}
return 0;
}
这有效( http://ideone.com/CFcVhu ),但是它并不那么漂亮...
#include <iostream>
#include <iomanip>
using namespace std;
int main(int argc, char **argv)
{
float testme[] = { 0.12345, 1.2345, 12.345, 123.45, 1234.5, 12345 };
//std::cout << std::setprecision(2) << std::fixed;
for(int i = 0; i < 6; ++i)
{
std::cout << ((int)(testme[i]*100.0))/100.0f << std::endl;
}
return 0;
}
换句话说,如果数字小于1000(总是为正),则要使用2个十进制数字表示;如果小于10000,则要使用1个十进制数字表示,否则为零。 嗯,一个人怎么能编成这样呢?
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