打印到c ++中在线的特定位置输出

Question

I am trying to print to a uniform position in a line after printing out a header. here's an example:

PHRASE                 TYPE
"hello there"       => greeting
"yo"                => greeting
"where are you?"    => question
"It's 3:00"         => statement
"Wow!"              => exclamation

Assume each of these are stored in a std::map<string, string> , where key = phrase and value = type. My issue is that simply using tabs is dependent on the console or text editor that I view the output in. If the tab width is too small I won't know for sure where it will be printed. I have tried using setw , but that only prints the separator ("=>") a fixed distance from the end of the phrase. Is there a simple way to do this?

NOTE Assume for now that we just always know that the phrase will not be longer than, say, 16 characters. We don't need to account for what to do if it is.

Answer 1

Use std::left and std::setw :

std::cout << std::left; // This is "sticky", but setw is not.
std::cout << std::setw(16) << phrase << " => " << type << "\n";

For example:

#include <iostream>
#include <string>
#include <iomanip>
#include <map>

int main()
{
    std::map<std::string, std::string> m;
    m["hello there"]    = "greeting";
    m["where are you?"] = "question";

    std::cout << std::left;

    for (std::map<std::string, std::string>::iterator i = m.begin();
         i != m.end();
         i++)
    {
        std::cout << std::setw(16)
                  << std::string("\"" + i->first + "\"")
                  << " => "
                  << i->second
                  << "\n";
    }
    return 0;
}

Output:

"hello there"    => greeting
"where are you?" => question

See http://ideone.com/JTv6na for demo.

Answer 2

printf("\"%s\"%*c => %s", 
    it->first.c_str(), 
    std::max(0, 16 - it->first.size()),
    ' ',
    it->second.c_str());`

The same idea as Peter's solution, but puts the padding outside the quotes. It uses %c with a length argument to insert padding.

Answer 3

If you're not adverse to C-style printing, printf is great for this sort of thing, and much more readable:

printf("\"%16s\" => %s\n", it->first.c_str(), it->second.c_str());

There's nothing wrong with using printf and friends in a C++ program, just be careful mixing iostreams and stdio. You can always sprintf into a buffer, then output that with iostreams.

Answer 4

You might find this function useful:

#include <iostream>
#include <iomanip>

void printRightPadded(std::ostream &stream,const std::string &s,size_t width)
{
  std::ios::fmtflags old_flags = stream.setf(std::ios::left);
  stream << std::setw(width) << s;
  stream.flags(old_flags);
}

You could use it like this:

void
  printKeyAndValue(
    std::ostream &stream,
    const std::string &key,
    const std::string &value
  )
{
  printRightPadded(stream,"\"" + key + "\"",18);
  stream << " => " << value << "\n";
}

Answer 5

如果你无法使用setw，一个简单的替代方法是用空格修补所有短语，这样它们都是16个字符长。

Answer 6

I personally find the C-style printing more readable for formatted printing. Using printf you could also handle the column width using the * formatter.

#include <cstdio>

int main() {
    printf("%-*s%-*s\n", 10, "Hello", 10, "World");
    printf("%-*s%-*s\n", 15, "Hello", 15, "World");  

    // in the above, '-' left aligns the field
    // '*' denotes that the field width is a parameter specified later
    // ensure that the width is specified before what it is used to print  
}

Output

Hello     World     
Hello          World