printing 2d table (headers) - c++

Question

Is there are a better way than this one to print 2d table?
std::cout
<< std::setw(25) << left << "FF.name"
<< std::setw(25) << left << "BB.name"
<< std::setw(12) << left << "sw.cycles"
<< std::setw(12) << left << "hw.cycles" << "\n"
<< std::setw(25) << left << "------"
<< std::setw(25) << left << "------"
<< std::setw(12) << left << "---------"
<< std::setw(12) << left << "---------" << "\n";

Answer 1

You could put the headers into an array or vector, then generate the correct widths automatically:
boost::array<std::string, 4> head = { ... }
BOOST_FOREACH(std::string& s, head)
{
int w = 5*(s.length()/5 + 1);
std::cout << std::setw(w) << left << s;
}
std::cout << '\n';
BOOST_FOREACH(std::string& s, head)
{
int w = 5*(s.length()/5 + 1);
std::cout << std::string(w,'-');
}
std::cout << std::endl;
Might be worthwhile if you have lots of headers I guess.

Answer 2

Use printf. It's part of C, but it's still supported in C++.

Answer 3

Break things up into functions and it's not so bad.
#include <iostream>
#include <iomanip>
#include <string>
#include <vector>
typedef std::vector< std::string > StringVector;
void printRow( std::ostream& s, const StringVector& strings )
{
s << std::setw(25) << std::left << strings[ 0 ];
s << std::setw(25) << std::left << strings[ 1 ];
s << std::setw(12) << std::left << strings[ 2 ];
s << std::setw(12) << std::left << strings[ 3 ];
s << "\n";
}
void printHeadings( std::ostream& s, const StringVector& headings )
{
printRow( s, headings );
StringVector lines;
for ( StringVector::const_iterator H = headings.begin();
H != headings.end();
++H )
{
lines.push_back( std::string( H->size(), '-' ) );
}
printRow( s, lines );
}
int main()
{
StringVector headings( 4 );
headings[ 0 ] = "FF.name";
headings[ 1 ] = "BB.name";
headings[ 2 ] = "sw.cycles";
headings[ 3 ] = "hw.cycles";
printHeadings( std::cout, headings );
StringVector contents( 4 );
contents[ 0 ] = "foo";
contents[ 1 ] = "bar";
contents[ 2 ] = "baz";
contents[ 3 ] = "foobarbaz";
printRow( std::cout, contents );
return 0;
}
Note that I've left out the bounds checking on the string vectors since this is only intended as an example.

Answer 4

Width is the only formatting setting that gets reset, so you can trivially simplify to:
std::cout << left;
std::cout
<< std::setw(25) << "FF.name"
<< std::setw(25) << "BB.name"
<< std::setw(12) << "sw.cycles"
<< std::setw(12) << "hw.cycles"
<< "\n";
You might like:
//...
std::cout << w(25, "FF.name");
//...
// implemented:
template<class T>
struct AtWidth {
std::streamsize width;
T const& obj;
AtWidth(std::streamsize width, T const& obj) : width(width), obj(obj) {}
template<class Stream> // easier than templating on basic_stream
friend Stream& operator<<(Stream& s, AtWidth const& value) {
s.width(value.width);
return s << value.obj;
}
};
template<class T>
AtWidth<T> w(std::streamsize width, T const& obj) {
return AtWidth<T>(width, obj);
}
Or if you want to rename the setw function (C++0x):
auto w(std::streamsize width) -> decltype(std::setw(width)) {
return std::setw(width);
}
// ...
std::cout << w(25) << "FF.name";
(In non-0x, you'd have to either know how your library implements setw to get the right type or re-write it yourself, which isn't too hard, BTW.)
Edit: I missed the second line of dashes here, another answer covers that well enough. The solution for that is indeed to construct a header "object" and print it out more or less at once.