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pprint: Pretty Printer for Modern C++

 4 years ago
source link: https://www.tuicool.com/articles/hit/YRV3m2I
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Highlights

  • Single header file
  • Requires C++17
  • MIT License

Quick Start

Simply include pprint.hpp and you're good to go.

#include <pprint.hpp>

To start printing, create a PrettyPrinter 

pprint::PrettyPrinter printer;

You can construct a PrettyPrinter with any stream that inherits from std::ostream , e.g, std::stringstream 

std::stringstream stream;
pprint::PrettyPrinter printer(stream);

Fundamental Types

printer.print(5);
printer.print(3.14f);
printer.print(2.718);
printer.print(true);
printer.print('x');
printer.print("Hello, 世界");
printer.print(nullptr);
5
3.14f
2.718
true
'x'
"Hello, 世界"
nullptr

Strings

Maybe you don't want your strings to be quoted? Simply set printer.quotes(false) 

printer.quotes(false);
printer.print('A', 'B', 'C');   // parameter packing
printer.print("1 2 3");
A B C
1 2 3

Complex Numbers

using namespace std::complex_literals;
std::complex<double> cfoo = 1. + 2.5i;
std::complex<double> cbar = 9. + 4i;
printer.print(cfoo, "*", cbar, "=", (cfoo * cbar));   // parameter packing
(1 + 2.5i) * (9 + 4i) = (-1 + 26.5i)

Enumeration Types

enum Color { RED = 2, BLUE = 4, GREEN = 8 };
Color color = BLUE;
printer.print(color);

If you compile with

  • Clang/LLVM >= 5
  • Visual C++ >= 15.3 / Visual Studio >= 2017
  • Xcode >= 10.2
  • GCC >= 9

then pprint will print the name of the enum for you (thanks to magic_enum ) 

enum Level { LOW, MEDIUM, HIGH };
Level current_level = MEDIUM;
std::cout << "Current level: ";
printer.print(current_level);
Current level: MEDIUM

STL Sequence Containers

pprint supports a variety of STL sequence containers including std::vector , std::list , std::deque , and std::array .

Here's an exmaple pretty print of a simple 3x3 matrix:

typedef std::array<std::array<int, 3>, 3> Mat3x3;
Mat3x3 matrix;
matrix[0] = {1, 2, 3};
matrix[1] = {4, 5, 6};
matrix[2] = {7, 8, 9};
printer.print(matrix);
[
  [1, 2, 3], 
  [4, 5, 6], 
  [7, 8, 9]
]

Compact Printing

pprint also supports compact printing of containers. Simply call printer.compact(true) to enable this: 

std::vector<std::map<std::string, int>> foo {{{"a", 1}, {"b", 2}}, {{"c", 3}, {"d", 4}}};
printer.compact(true);
std::cout << "Foo = ";
printer.print(foo);
Foo = [{"a" : 1, "b" : 2}, {"c" : 3, "d" : 4}]

STL Associative Containers

Support for associative containers includes pretty printing of std::map , std::multimap , std::unordered_map , std::unordered_multimap , std::set , std::multiset , std::unordered_set and , std::unordered_multiset 

printer.print(std::map<std::string, std::set<int>>{ 
    {"foo", {1, 2, 3, 3, 2, 1}}, {"bar", {7, 6, 5, 4}}});
{
  "bar" : {4, 5, 6, 7}, 
  "foo" : {1, 2, 3}
}

STL Container Adaptors

pprint can print container adaptors including std::queue , std::priority_queue and std::stack . Here's an example print of a priority queue: 

std::priority_queue<int> queue;
for(int n : {1,8,5,6,3,4,0,9,7,2})
  queue.push(n);
printer.print(queue);
[9, 8, 7, 6, 5, 4, 3, 2, 1, 0]

Fixed-size Heterogeneous Tuples

auto get_student = [](int id) {
  if (id == 0) return std::make_tuple(3.8, 'A', "Lisa Simpson");
  if (id == 1) return std::make_tuple(2.9, 'C', "Milhouse Van Houten");
  if (id == 2) return std::make_tuple(1.7, 'D', "Ralph Wiggum");
  throw std::invalid_argument("id");
};
printer.print({ get_student(0), get_student(1), get_student(2) });
{(1.7, 'D', "Ralph Wiggum"), (2.9, 'C', "Milhouse Van Houten"), (3.8, 'A', "Lisa Simpson")}

Type-safe Unions

// Construct a vector of values
std::vector<std::variant<bool, int, int *, float, std::string, std::vector<int>,		      
       std::map<std::string, std::map<std::string, int>>, 
       std::pair<double, double>>> var;
var.push_back(5);
var.push_back(nullptr);
var.push_back(3.14f);
var.push_back(std::string{"Hello World"});
var.push_back(std::vector<int>{1, 2, 3, 4});
var.push_back(std::map<std::string, std::map<std::string, int>>{{"a",{{"b",1}}}, {"c",{{"d",2}, {"e",3}}}});
var.push_back(true);
var.push_back(std::pair<double, double>{1.1, 2.2});

// Print the vector
pprint::PrettyPrinter printer;
printer.indent(2);
printer.print(var);
[
  5, 
  nullptr,
  3.14f, 
  "Hello World", 
  [1, 2, 3, 4], 
  {"a" : {"b" : 1}, "c" : {"d" : 2, "e" : 3}}, 
  true, 
  (1.1, 2.2)
]

Optional Values

std::optional<int> opt = 5;
std::optional<int> opt2;

printer.print(opt);
printer.print(opt2);
5
nullopt

Class Objects

pprint print class objects with or without an overloaded << operator 

class Foo {};
Foo foo;
printer.print(foo);
<Object main::Foo at 0x7ffc8c820890>

If an << operator is available, pprint will use it to print your object: 

class Date {
  unsigned int month, day, year;
public:
  Date(unsigned int m, unsigned int d, unsigned int y) : month(m), day(d), year(y) {}
  friend std::ostream& operator<<(std::ostream& os, const Date& dt);
};

    
std::ostream& operator<<(std::ostream& os, const Date& dt) {
  os << dt.month << '/' << dt.day << '/' << dt.year;
  return os;
}
Date date(04, 07, 2019);
std::cout << "Today's date is ";
printer.print(date);
Today's date is 4/7/2019

License

The project is available under the MIT license.


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