C++ 如何将整个流读入 std::string？
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How to read entire stream into a std::string?
提问by Roddy
I'm trying to read an entire stream (multiple lines) into a string.
我正在尝试将整个流（多行）读入一个字符串。
I'm using this code, and it works, but it's offending my sense of style... Surely there's an easier way? Maybe using stringstreams?
我正在使用这段代码，它可以工作，但它冒犯了我的风格……当然有更简单的方法吗？也许使用字符串流？
void Obj::loadFromStream(std::istream & stream)
{
std::string s;
std::streampos p = stream.tellg(); // remember where we are
stream.seekg(0, std::ios_base::end); // go to the end
std::streamoff sz = stream.tellg() - p; // work out the size
stream.seekg(p); // restore the position
s.resize(sz); // resize the string
stream.read(&s[0], sz); // and finally, read in the data.
实际上，
constconst对字符串的引用也可以，这可能会使事情变得更容易......const std::string &s(... a miracle occurs here...)
回答by Cubbi
How about
怎么样
std::istreambuf_iterator<char> eos;
std::string s(std::istreambuf_iterator<char>(stream), eos);
(could be a one-liner if not for MVP)
（如果不是MVP，可能是单线）
post-2011 edit, this approach is now spelled
2011 年之后的编辑，这种方法现在拼写
std::string s(std::istreambuf_iterator<char>(stream), {});
回答by Joey Adams
I'm late to the party, but here is a fairly efficient solution:
我迟到了，但这是一个相当有效的解决方案：
std::string gulp(std::istream &in)
{
std::string ret;
char buffer[4096];
while (in.read(buffer, sizeof(buffer)))
ret.append(buffer, sizeof(buffer));
ret.append(buffer, in.gcount());
return ret;
}
I did some benchmarking, and it turns out that the std::istreambuf_iteratortechnique (used by the accepted answer) is actually much slower. On gcc 4.4.5 with -O3, it's about a 4.5x difference on my machine, and the gap becomes wider with lower optimization settings.
我做了一些基准测试，结果发现该std::istreambuf_iterator技术（被接受的答案使用）实际上要慢得多。在带有 的 gcc 4.4.5 上-O3，在我的机器上大约有 4.5 倍的差异，并且随着优化设置的降低，差距变得更大。
回答by Matteo Italia
You could do
你可以做
std::string s;
std::ostringstream os;
os<<stream.rdbuf();
s=os.str();
but I don't know if it's more efficient.
但我不知道它是否更有效率。
Alternative version:
替代版本：
std::string s;
std::ostringstream os;
stream>>os.rdbuf();
s=os.str();
回答by wheaties
You can try using something from algorithms. I have to get ready for work but here's a very quick stab at things (there's got to be a better way):
您可以尝试使用算法中的某些内容。我必须为工作做好准备，但这里有一个非常快速的尝试（必须有更好的方法）：
copy( istreambuf_iterator<char>(stream), istreambuf_iterator<char>(), back_inserter(s) );
回答by wdavilaneto
Well, if you are looking for a simple and 'readable' way to do it. I would recomend add/use some high level framework on your project. For that I's always use Poco and Boost on all my projects. In this case, with Poco:
好吧，如果您正在寻找一种简单且“可读”的方式来做到这一点。我建议在您的项目中添加/使用一些高级框架。为此，我总是在我所有的项目中使用 Poco 和 Boost。在这种情况下，使用 Poco：
string text;
FileStream fstream(TEXT_FILE_PATH);
StreamCopier::copyToString(fstream, text);
回答by user7223715
Perhaps this 1 line C++11 solution:
也许这 1 行 C++11 解决方案：
std::vector<char> s{std::istreambuf_iterator<char>{in},{}};
