C ++等效于C格式“％3d”？

Question

My code is:

#include<iostream>
using namespace std;
int main()
{
    int count=0;
    int total=0;

    while(count<=10)
    {   
        total=total+count;   
        cout<<"count"<<"="<<count/*<<','*/<<'\t'<<'\t'<<"total"<<"="<<total<<endl;
        count++;
    }
}

Answer 1

All of the facilities of the C standard library are still available in C++. You can write your program like this:

#include <cstdio>
using std::printf;

int main()
{
  int count = 0;
  int total = 0;

  while (count<=10)
  {   
    total = total + count;
    printf("count=%3d, total=%3d\n", count, total); 
    count++;
  }
}

It is my personal opinion that the stdio.h output interfaces are nearly always easier to use and produce more readable code than the iostream output interfaces, particularly for formatted output of numbers (as in this case), so I would not hesitate to do so. The major advantage of iostream is that it can be extended to format objects via operator<< overloads, but a program like this does not need that.

Note that neither the stdio.h nor the iostream input interfaces are fit for purpose, due to egregious, standard-codified bugs like defining numeric input overflow to trigger undefined behavior (I am not making this up!)

Answer 2

Using iostream formatting, you need to include the iomanip header and use the setw and setfill , like this:

#include <iostream>
#include <iomanip>

int main() {
    using namespace std;

    int count=0;
    int total=0;

    while(count<=10)
    {   
        total=total+count;   
        cout<<"count"<<"="<<count<<'\t'<<'\t'<<"total"<<"="<<setfill(' ')<<setw(3)<<total<<endl;
        count++;
    }
}

Answer 3

You can use setw and left from iomanip to achive the effect you want.

#include <iostream>
#include <iomanip>

int main()
{
    int count=0;
    int total=0;

    while(count<=10)
    {
        total=total+count;
        std::cout << "count = " << std::setw(15) << std::right << count << "total = " << total << std::endl;
        count++;
    }
}

setw set the with of the next "cout impression" (15 in this case) and left just set the aligment to the left.

Note: As suggest by @Zack you can write << '\\n' at the end instead << endl . Since << endl is exactly the same as writing << '\\n' << flush and the flush isn't necessary in this case.

Answer 4

In C++ IO formatting is being done either in same way as in C (since all C functionalities are in place also in C++) or with std::setw std::setprecission and other C++ manipulators presented in header .

So either of this will be fine:

#include <cstdio>

int main()
{
    int count=0;
    int total=0;

    while( count <= 10)
    {
        total += count;
        printf( "count = %3d, total = %3d\n", count++, total);
    }
}

or

#include <iostream>
#include <iomanip>

int main()
{
    int count=0;
    int total=0;

    while( count <= 10)
    {
        total += count;
        std::cout << "count = " << std::setw(15) << 
                        count++ << "total = " << total << std::endl;
    }
    return 0;
}

You can also do custom formatting by imbue to apply custom facet to locale ( ie extend std::numpunct).

http://ideone.com/nHfTL6