Cygwin g ++不识别“固定”作为STD库的一部分

Question

I'm an amateur with C++ and I'm learning to compile by command line using g++. I downloaded and installed Cygwin and I can't get this code to work:

// setprecision example
#include <iostream>     // std::cout, std::fixed
#include <iomanip>      // std::setprecision

int main () {
  double f =3.14159;
  std::cout << std::setprecision(5) << f << '\n';
  std::cout << std::setprecision(9) << f << '\n';
  std::cout << std::fixed;
  std::cout << std::setprecision(5) << f << '\n';
  std::cout << std::setprecision(9) << f << '\n';
return 0;

}

But when I run the console

g++ -c Test.cpp

I get the error:

Test.cpp: In function `int main()':
Test.cpp:9: undeclared variable `fixed' (first use here)

Can anyone explain where the error comes from and how I can fix it? I tried

#include <ios>

at the top of my program but it tells me that the file/directory can't be found. In the include\\g++\\ subfolder of my Cygnus program I have an iomanip.h and iostream file but no ios file.

Answer 1

You need #include <ios> . iostream is not required to include very much, and needn't declare fixed .