字符串格式化（c ++） [英] String formatting (c++)

问题描述

我尝试在控制台应用程序中格式化输出字符串（如表格）

  cout< \\\
\\\
 ----------------- \\\
; 
 cout<< setw（8）<<左< F\t |; 
 cout<< setw（8）<<左< x\t |; 
 cout<< \\\
 ----------------- \\\
; 
 // ... 
 cout.width（8）; 
 cout.setf（ios :: left）; 
 cout<<固定< setprecision（3）<< F<< \t |; 
 
 cout.width（8）; 
 cout.setf（ios :: left）; 
 cout<< x < \t |; 
 cout<< \\\
 ----------------- \\\
\\\
; 
  

但结果我的输出看起来像这样



我的上部字符串格式有什么问题？

我会不是

em>停止只是删除选项卡。因为它现在，你的代码是高度重复的，接近不可能维护。我会做一个（几乎）完全重写，有几个功能，以减少重复。我的第一个剪切可能看起来像这样：

  //在指定宽度的字段中格式化一个值， 
 template< class T> 
 string字段（T val，int w，char sep ='|'）{
 stringstream b; 
 b<< setw（w）左<固定< setprecision（3）<< val<< sep; 
 return b.str（）; 
} 
 
 //为指定数量的字段生成分隔符
 //每个指定宽度
 string sep（int c，int w，char val =' - '）{
 string s（c *（w + 1），val）; 
 return string（\\\
）+ s +\\\
; 
} 
 
 int main（）{
 static const int w = 8; 
 double F = 1.234，x = 3.45; 
 string s = sep（2，w）; 
 
 cout<< \\\
< s; 
 cout<<字段（F，w）<字段（x，w） s; 
 cout<<字段（F，w）字段（x，w） s; 
} 
  

看起来这让代码更容易阅读，可维护。例如，如果我们决定在下一行显示 a 和 b 例如：

  cout<字段（a，w）字段（b，w） s; 
  

...我们不必看起来很难以确定它会匹配上一行。同样，如果我们想更改列宽等，

I tried to format output strings in my console application (like a table)

cout <<  "\n\n-----------------\n";
cout << setw(8) << left << "F\t|";
cout << setw(8) << left << "x\t|";
cout <<  "\n-----------------\n";
//...
cout.width(8);
cout.setf(ios::left);
cout << fixed << setprecision(3) << F << "\t|";

cout.width(8);
cout.setf(ios::left);
cout << x << "\t|";
cout <<  "\n-----------------\n\n";

But as result my output looks like this

What's wrong with my upper string formatting?

解决方案

As already noted, it's the tabs that are causing the problem.

I would not stop at just removing the tabs though. As it stands right now, your code is highly repetitive and next to impossible to maintain. I'd do a (nearly) complete rewrite, with a couple of functions to cut down on the repetition. My first cut would probably look something like this:

// format a value in a field of specified width, followed by a separator
template <class T>
string field(T val, int w, char sep = '|') {
    stringstream b;
    b << setw(w) << left << fixed << setprecision(3) << val << sep;
    return b.str();
}

// generate a separator for a specified number of fields,
// each of a specified width
string sep(int c, int w, char val = '-') {
    string s(c * (w + 1), val);
    return string("\n") + s + "\n";
}

int main() {
    static const int w = 8;
    double F = 1.234, x = 3.45;
    string s = sep(2, w);

    cout << "\n" << s;
    cout << field("F", w) << field("x", w) << s;
    cout << field(F, w) << field(x, w) << s;
}

Seems to me that this makes the code rather more readable and quite a bit more maintainable. For example, if we decided to display an a and b on the next line, it would seem fairly obvious to add something like:

cout << field(a, w) << field(b, w) << s;

...and we wouldn't have to look very hard to be pretty sure it was going to match up with the previous line. Likewise, if we wanted to change a column width, etc.

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