假设我有一个字符向量,我将其作为字符串推入流中,而不是字符向量,我将如何使用运算符>>取回字符向量?
class C{
private:
vector<char> c;
public:
C(string str){
for(int x = 0; x < str.size(); x++)
c.push_back(str[x]);
}
vector<char> data(){
return c;
}
};
ostream operator<<(ostream & stream, C & in){
for(int x = 0; x < in.data().size(); x++)
stream << in.data()[x];
return stream;
}
istream operator>>(istream & stream, C & in){
// ???
// what kind of loop?
}
答案 0 :(得分:3)
我会像这样写你的例子......
#include <algorithm>
#include <iterator>
#include <vector>
#include <iostream>
#include <sstream>
class C
{
std::vector<char> mData;
public:
// Constructor, note im using the iterator range
// vector constructor.
C(const std::string& str)
: mData(str.begin(), str.end())
{
}
// Returning data by const reference to avoid
// copying a potentially large object.
const std::vector<char>& data() const
{
return mData;
}
// declared the input operator as a friend as I need it to
// access mData - alternatively you could write a "loadFromStream"
// type function that does the same, declare this as non-friend, and call that.
friend std::istream& operator>>(std::istream& is, C& c);
};
std::ostream& operator<<(std::ostream& os, const C& c)
{
// Use an ostream_iterator to handle output of the vector
// using iterators.
std::copy(c.data().begin(),
c.data().end(),
std::ostream_iterator<char>(os, ""));
return os;
}
std::istream& operator>>(std::istream& is, C& c)
{
// load the data using the assign function, which
// clears any data already in the vector, and copies
// in the data from the specified iterator range.
// Here I use istream_iterators, which will read to the end
// of the stream. If you dont want to do this, then you could
// read what you want into a std::string first and assign that.
c.mData.assign(std::istream_iterator<char>(is),
std::istream_iterator<char>());
return is;
}
int main()
{
C c("Hello");
std::stringstream ss;
ss << c;
std::cout << ss.str() << std::endl;
C d("");
ss >> d;
std::cout << d.data().size() << std::endl;
return 0;
}
答案 1 :(得分:2)
你总是可以从另一个构建一个:
std::vector<char> A = getVector();
std::string B = getString();
std::vector<char> newB(B.begin(), B.end());
std::string newA(A.begin(), A.end());
使用它你应该能够编写你的插播操作符,例如
std::string stmp;
stream >> stmp;
std::vector<char> vtmp(stmp.begin(), stmp.end());
c.swap(vtmp);
答案 2 :(得分:1)
做什么&gt;&gt; std::string
的确如此,你真的需要使用std::string
。请注意,您需要通过引用而不是值传递C
,并且运算符应该通过引用返回原始流。另外,我不禁想到使用std::vector<char>
代替std::string
并不是那么有用(另外,ctor效率低下 - 至少保留str.length()
如果你这样做)。
istream& operator>>(istream& s, C& in) {
std::string tmp;
s >> tmp;
// you also need to return reference in in.data() for this to work
// or declare operator>> as friend and use in.c directly
in.data().assign(tmp.begin(), tmp.end());
return s;
}
答案 3 :(得分:1)
首先,您需要将您的流作为引用而不是按值返回。此外,data()
应返回对向量的const引用,以便不复制它(如果它是一个大向量,则很重要)。
至于重载&gt;&gt;,我会尝试类似:
istream& operator>>(istream& stream, C& in) {
for (char c; /* some end condition */;) {
stream >> c;
in.c.push_back(c);
}
}
当然,这种方法需要声明operator>>(istream&, C&)
朋友的功能。另一种方法是向公共接口提供等效的append(char)
函数。此外,data()
应标记为const,因此整个签名将为const vector<char>& data() const
,表明它严格来说是一个访问者。
答案 4 :(得分:1)
您可以使用istream迭代器。 它的默认构造函数初始化为流的结尾。
http://www.cplusplus.com/reference/std/iterator/istream_iterator/
您的代码看起来就像。
typedef std::istream_iterator<char> charstream_it;
c = std::vector<char>(charstream_it(stream), charstream_it());
在构造函数中,您可能应该使用Kerrek SB建议的STL迭代器样式复制构造函数。
C::C(string str):
c(str.begin(), str.end()) {};