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  1. #include <iostream>
  2. #include <vector>
  3. #include <string>
  4.  
  5. struct T {
  6. 	T() = default;
  7. 	T(int i, double d, const std::string& s) : i_(i), d_(d), s_(s) {}
  8. 	int i_;
  9. 	double d_;
  10. 	std::string s_;
  11. 	friend std::ostream& operator << (std::ostream& to, const T& t) {
  12. 		return to << '[' << t.i_ << ',' << t.d_ << ',' << t.s_ << ']';
  13. 	}
  14. };
  15.  
  16. using TVec = std::vector<T>;
  17.  
  18. void status(const char* label, const TVec& tv)
  19. {
  20. 	std::cout << label << ":\n";
  21. 	std::cout << "tv.empty() == " << (tv.empty() ? "true" : "false") << "\n";
  22. 	if (tv.empty() == false) {
  23. 		std::cout << "+  tv.front() == " << tv.front() << "\n";
  24. 		std::cout << "+  tv.back() == " << tv.back() << "\n";
  25. 	}
  26. 	std::cout << "tv.capacity() == " << tv.capacity() << "\n";
  27. 	std::cout << "tv.size() == " << tv.size() << "\n";
  28. 	std::cout << "\n";
  29. }
  30.  
  31.  
  32. int main() {
  33. 	TVec tv;
  34.  
  35. 	status("start", tv);
  36.  
  37. 	tv.reserve(10);  // pre-allocate room for 10.
  38. 	status("after reserve", tv);
  39.  
  40. 	tv.emplace_back(0, 42., "first");
  41. 	status("after first", tv);
  42.  
  43. 	{
  44. 		T temp { 1, 42., "second" };
  45. 		tv.push_back(temp);  // copy temp to new entry in tv.
  46. 	}
  47. 	status("after second", tv);
  48.  
  49. 	tv.emplace_back(2, 50., "third");
  50. 	status("after third", tv);
  51.  
  52. 	std::cout << "tv[1].s_ = " << tv[1].s_ << "\n";
  53.  
  54. 	// C++'s standard library heavily uses something called "iterators",
  55. 	// these are variables that reference entries in a container like a
  56. 	// vector. An iterator lets you ask a question like "find me an element
  57. 	// with this value" or "tell me the start and end of a range".
  58. 	// The most natural range is the start and end of the container.
  59. 	// These are `begin` and `end`. `begin` references the first element
  60. 	// while `end` references *beyond* the last element. This is an
  61. 	// important distinction because it lets you determine if something is
  62. 	// *not* in a container.
  63.  
  64. 	std::cout << "Contents of tv using iterators:\n";
  65. 	for (auto it = tv.begin(); it != tv.end(); ++it) {
  66. 		// "it" is the iterator itself, like a pointer,
  67. 		// "*it" is the entry the iterator references.
  68. 		std::cout << "  " << *it << "\n";
  69. 	}
  70.  
  71. 	// there's also insertion: here we'll insert infront of the first entry
  72. 	tv.insert(tv.begin(), T { -1, -1., "sneaky" });
  73. 	status("after sneaky", tv);
  74.  
  75. 	std::cout << "Contents of tv using range-based for:\n";
  76. 	for (auto&& t : tv) {
  77. 		// 'auto t' would *copy* every T in tv into `t`, which is wasteful,
  78. 		// 'auto&& t' will use a reference if it can, which saves cpu
  79. 		std::cout << "  " << t << "\n";  // note no need to do '*'.
  80. 	}
  81.  
  82. 	// now lets remove the element *after* sneaky
  83. 	tv.erase(tv.begin() + 1);
  84. 	status("after erase", tv);
  85.  
  86. 	// finally, one last magical function
  87. 	tv.clear();
  88. 	status("after clear", tv);
  89. }
  90.  
Success #stdin #stdout 0s 3476KB
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Standard input is empty
stdout
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start:
tv.empty() == true
tv.capacity() == 0
tv.size() == 0

after reserve:
tv.empty() == true
tv.capacity() == 10
tv.size() == 0

after first:
tv.empty() == false
+  tv.front() == [0,42,first]
+  tv.back() == [0,42,first]
tv.capacity() == 10
tv.size() == 1

after second:
tv.empty() == false
+  tv.front() == [0,42,first]
+  tv.back() == [1,42,second]
tv.capacity() == 10
tv.size() == 2

after third:
tv.empty() == false
+  tv.front() == [0,42,first]
+  tv.back() == [2,50,third]
tv.capacity() == 10
tv.size() == 3

tv[1].s_ = second
Contents of tv using iterators:
  [0,42,first]
  [1,42,second]
  [2,50,third]
after sneaky:
tv.empty() == false
+  tv.front() == [-1,-1,sneaky]
+  tv.back() == [2,50,third]
tv.capacity() == 10
tv.size() == 4

Contents of tv using range-based for:
  [-1,-1,sneaky]
  [0,42,first]
  [1,42,second]
  [2,50,third]
after erase:
tv.empty() == false
+  tv.front() == [-1,-1,sneaky]
+  tv.back() == [2,50,third]
tv.capacity() == 10
tv.size() == 3

after clear:
tv.empty() == true
tv.capacity() == 10
tv.size() == 0
https://ideone.com/HERvy1
language:
C++14 (gcc 8.3)
created:
7 years ago
visibility:
public

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