Table layout using std::cout

Question

How do I format my output in C++ streams to print fixed width left-aligned tables? Something like

printf("%-14.3f%-14.3f\n", 12345.12345, 12345.12345);

poducing

12345.123     12345.123

Answer 1

Include the standard header <iomanip> and go crazy. Specifically, the setw manipulator sets the output width. setfill sets the filling character.

Answer 2

std::cout << std::setiosflags(std::ios::fixed)
          << std::setprecision(3)
          << std::setw(18)
          << std::left
          << 12345.123;

Answer 3

You may also consider more friendly functionality provided by one of these:

• Boost.Format (powerful, but very heavy, more time and memory allocations than other mentioned)
• Loki.SafeFormat
• FastFormat (relatively new, but blazing fast library, also type-safe unlike the others)

Writing from memory, but should be something along these lines:

// Dumb streams:
printf("%-14.3f%-14.3f\n", 12345.12345, 12345.12345);

// For IOStreams you've got example in the other answers

// Boost Format supports various flavours of formatting, for example:
std::cout << boost::format("%-14.3f%-14.3f\n") % a % b;
std::cout << boost::format("%1$-14.3f%2$-14.3f\n") % a % b;
// To gain somewhat on the performance you can store the formatters:
const boost::format foo("%1$-14.3f%2$-14.3f\n");
std::cout << boost::format(foo) % a % b;

// For the Loki::Printf it's also similar:
Loki::Printf("%-14.3f%-14.3f\n")(a)(b);

// And finally FastFormat.Format (don't know the syntax for decimal places)
fastformat::fmtln(std::cout, "{0,14,,<}{1,14,,>}", a, b);

Also, if you plan to stick with any of these formatting libraries, examine thoroughly their limitations in context of expressibility, portability (and other library dependency), efficiency, support of internationalisation, type-safety, etc.