如何将std::vector的内容打印到屏幕上?
实现以下操作符<<的解决方案也很好:
template<container C, class T, String delim = ", ", String open = "[", String close = "]">
std::ostream & operator<<(std::ostream & o, const C<T> & x)
{
// ... What can I write here?
}
以下是目前为止我所做的，没有单独的函数:
#include <iostream>
#include <fstream>
#include <string>
#include <cmath>
#include <vector>
#include <sstream>
#include <cstdio>
using namespace std;
int main()
{
ifstream file("maze.txt");
if (file) {
vector<char> vec(istreambuf_iterator<char>(file), (istreambuf_iterator<char>()));
vector<char> path;
int x = 17;
char entrance = vec.at(16);
char firstsquare = vec.at(x);
if (entrance == 'S') {
path.push_back(entrance);
}
for (x = 17; isalpha(firstsquare); x++) {
path.push_back(firstsquare);
}
for (int i = 0; i < path.size(); i++) {
cout << path[i] << " ";
}
cout << endl;
return 0;
}
}
我认为最好的方法是通过在程序中添加这个函数来重载操作符<<:
#include <vector>
using std::vector;
#include <iostream>
using std::ostream;
template<typename T>
ostream& operator<< (ostream& out, const vector<T>& v) {
out << "{";
size_t last = v.size() - 1;
for(size_t i = 0; i < v.size(); ++i) {
out << v[i];
if (i != last)
out << ", ";
}
out << "}";
return out;
}
然后你可以在任何可能的向量上使用<<运算符，假设它的元素也定义了ostream&运算符<<:
vector<string> s = {"first", "second", "third"};
vector<bool> b = {true, false, true, false, false};
vector<int> i = {1, 2, 3, 4};
cout << s << endl;
cout << b << endl;
cout << i << endl;
输出:
{first, second, third}
{1, 0, 1, 0, 0}
{1, 2, 3, 4}
我认为最好的方法是通过在程序中添加这个函数来重载操作符<<:
#include <vector>
using std::vector;
#include <iostream>
using std::ostream;
template<typename T>
ostream& operator<< (ostream& out, const vector<T>& v) {
out << "{";
size_t last = v.size() - 1;
for(size_t i = 0; i < v.size(); ++i) {
out << v[i];
if (i != last)
out << ", ";
}
out << "}";
return out;
}
然后你可以在任何可能的向量上使用<<运算符，假设它的元素也定义了ostream&运算符<<:
vector<string> s = {"first", "second", "third"};
vector<bool> b = {true, false, true, false, false};
vector<int> i = {1, 2, 3, 4};
cout << s << endl;
cout << b << endl;
cout << i << endl;
输出:
{first, second, third}
{1, 0, 1, 0, 0}
{1, 2, 3, 4}
我将在这里添加另一个答案，因为我已经提出了与之前的方法不同的方法，那就是使用locale facet。
基本原理在这里
基本上你要做的是:
Create a class that derives from std::locale::facet. The slight downside is that you will need a compilation unit somewhere to hold its id. Let's call it MyPrettyVectorPrinter. You'd probably give it a better name, and also create ones for pair and map.
In your stream function, you check std::has_facet< MyPrettyVectorPrinter >
If that returns true, extract it with std::use_facet< MyPrettyVectorPrinter >( os.getloc() )
Your facet objects will have values for the delimiters and you can read them. If the facet isn't found, your print function (operator<<) provides default ones. Note you can do the same thing for reading a vector.
我喜欢这种方法，因为你可以使用默认打印，同时仍然能够使用自定义覆盖。
缺点是如果在多个项目中使用facet，则需要一个面向facet的库(因此不能仅仅是头文件)，而且需要注意创建一个新的locale对象的开销。
我把这个作为一个新的解决方案来写，而不是修改我的另一个解决方案，因为我相信两种方法都是正确的，你可以选择。
使用std::copy，但没有额外的尾随分隔符
使用std::copy的替代/修改方法(最初在@JoshuaKravtiz answer中使用)，但没有在最后一个元素后面包含额外的尾随分隔符:
#include <algorithm>
#include <iostream>
#include <iterator>
#include <vector>
template <typename T>
void print_contents(const std::vector<T>& v, const char * const separator = " ")
{
if(!v.empty())
{
std::copy(v.begin(),
--v.end(),
std::ostream_iterator<T>(std::cout, separator));
std::cout << v.back() << "\n";
}
}
// example usage
int main() {
std::vector<int> v{1, 2, 3, 4};
print_contents(v); // '1 2 3 4'
print_contents(v, ":"); // '1:2:3:4'
v = {};
print_contents(v); // ... no std::cout
v = {1};
print_contents(v); // '1'
return 0;
}
用于自定义POD类型容器的示例:
// includes and 'print_contents(...)' as above ...
class Foo
{
int i;
friend std::ostream& operator<<(std::ostream& out, const Foo& obj);
public:
Foo(const int i) : i(i) {}
};
std::ostream& operator<<(std::ostream& out, const Foo& obj)
{
return out << "foo_" << obj.i;
}
int main() {
std::vector<Foo> v{1, 2, 3, 4};
print_contents(v); // 'foo_1 foo_2 foo_3 foo_4'
print_contents(v, ":"); // 'foo_1:foo_2:foo_3:foo_4'
v = {};
print_contents(v); // ... no std::cout
v = {1};
print_contents(v); // 'foo_1'
return 0;
}
你可以使用std::experimental::make_ostream_joiner:
#include <algorithm>
#include <experimental/iterator>
#include <iostream>
#include <iterator>
#include <numeric>
#include <vector>
int main()
{
std::vector<int> vi(12);
std::iota(vi.begin(), vi.end(), -5);
std::cout << "Int vector:\n";
std::copy(std::begin(vi),
std::end(vi),
std::experimental::make_ostream_joiner(std::cout, ", "));
std::cout <<"\nString vector:\n[";
std::vector<std::string> vs { "some", "string", "vector" };
std::copy(std::begin(vs),
std::end(vs),
std::experimental::make_ostream_joiner(std::cout, "] - ["));
std::cout << "]\n";
}
Godbolt演示
