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

Solution 1

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

Solution 2

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

Solution 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.

Solution 4

You want to use stream manipulators:

http://www.deitel.com/articles/cplusplus_tutorials/20060218/index.html

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Comments

[Anonymous]

Links now, examples tomorrow afternoon (GMT time)

[R. Martinho Fernandes]

Don't forget std::left for the left-alignment.

[Iharob Al Asimi]

Is there a good reason why printf() wouldn't be a good choice?

[Konrad Rudolph]

@iharob The OP didn't ask for printf. That said, printf is a bad choice in C++ because it only handles builtin types, not user-defined types. It's also not type safe and allows potentially security relevant bugs to go undetected.