[英]Configuring std::ofstream format for floating point numbers
Is there a way to configure ostream using iomanip to output floating point numbers as follows: 有没有一种方法可以使用iomanip配置ostream来输出浮点数,如下所示:
0.00000000000000E+0000 0.00000000000000E + 0000
3.99147034531211E-0003 3.99147034531211E-0003
... ...
I am translating code from pascal to C++ and I need to output numbers in exactly same format. 我正在将代码从pascal转换为C ++,我需要以完全相同的格式输出数字。 It is preferable to use std::ofstream instead of fprintf or other C library functions.
最好使用std :: ofstream代替fprintf或其他C库函数。
One way to do this is with some string manipulation. 一种方法是使用一些字符串操作。 Format to a stringstream using scientific notation, then split the string on the 'e'.
使用科学计数法格式化为字符串流,然后在'e'上分割字符串。 Now you have the parts you can format yourself.
现在,您拥有了可以自行格式化的部分。
#include <iostream>
#include <iomanip>
#include <sstream>
#include <string>
std::string format(double val)
{
std::ostringstream oss;
oss << std::scientific << std::setprecision(14) << val;
auto result = oss.str();
auto match = result.find('e');
if (match == std::string::npos)
{
// Should never get here -- maybe throw
}
oss.str("");
auto exp = std::stoi(result.substr(match+1));
oss << result.substr(0, match) << 'E'
<< std::setw(5) << std::setfill('0')
<< std::internal << std::showpos << exp;
result = oss.str();
return result;
}
int main()
{
std::cout << format(3.99147034531211e-3) << '\n';
std::cout << format(6.02214085774e23) << '\n';
}
Output: 输出:
3.99147034531211E-0003
6.02214085774000E+0023
You will need to use std::fixed
您将需要使用
std::fixed
Sample program: 示例程序:
#include <iostream>
#include <fstream>
int main()
{
float f1 = -187.33667, f2 = 0.0;
std::ofstream out("test.bin",std::ios_base::binary);
if(out.good())
{
std::cout << "Writing floating point number: " << std::fixed << f1 << std::endl;
out.write((char *)&f1,sizeof(float));
out.close();
}
std::ifstream in("test.bin",std::ios_base::binary);
if(in.good())
{
in.read((char *)&f2,sizeof(float));
std::cout << "Reading floating point number: " << std::fixed << f2 << std::endl;
}
return 0;
}
OP by user Texan40. 用户Texan40的OP。 For more info: Here
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