C++ 将字符串或字符* 放入 istream 的最佳方法？
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Optimal way to get a string or char* into an istream?
提问by kal
What is the most optimal way to get a string or char* pointer into an istream.
将字符串或 char* 指针放入 istream 的最佳方法是什么。
I want to do the following
我想做以下事情
std::string a = "abc..";
//I know this can be done, not sure if this is most efficient
// and not sure about char* pointers
std::istringstream istr (a);
...
foo (istr);
void foo(std::istream& is) {
}
回答by Johannes Schaub - litb
If you want to construct an istringstream from it, a char* up to the null character, or all the stuff from an std::string:
如果你想从中构造一个 istringstream，一个 char* 到空字符，或者来自 std::string 的所有东西：
istringstream str(ptr); // char*
istringstream str(other_str); // std::string
If you talk about wanting a raw pointer into the buffer of an istream, you can't do it. Streams get their data on-demand if they need them either from files, terminals or else, optionally buffering their stuff (well, not exactly right. You can use a strstream, which accepts a raw pointer and reads/writes directly from that. But it's a deprecated class - don't use it. I'm lucky i've never done so). If all you want is something you can use somewhat like a pointer, you can use streambuf iterators. They are not really pointers though, so you can't subtract endfrom beginand other stuffs:
如果你说想要一个原始指针进入 istream 的缓冲区，你就做不到。如果流需要从文件、终端或其他方式获取它们的数据，则可以按需获取它们的数据，可选择缓冲它们的内容（嗯，不完全正确。您可以使用 a strstream，它接受原始指针并直接从中读取/写入。但它是不推荐使用的类 - 不要使用它。我很幸运我从来没有这样做过）。如果你想要的只是你可以像指针一样使用的东西，你可以使用流缓冲迭代器。不过，它们并不是真正的指针，因此您不能end从begin和其他东西中减去：
std::istreambuf_iterator<char> begin(one_istream), end;
while(begin != end)
std::cout << *begin++;
If you talk about getting a string out of what was written into a stringstream, you can use ostringstream::str:
如果您谈论从写入字符串流的内容中获取字符串，您可以使用ostringstream::str：
ostringstream o;
o << "This is a number: " << 42;
std::string str = o.str(); // str == "This is a number: 42"
Otherwise, you can only generally readstuff from an istream. You need an ostream, then you can do
否则，你一般只能读取来自东西istream。你需要一个ostream，然后你可以做
stream.write(ptr, N);
stream.write(ptr.c_str(), ptr.c_str() + ptr.size());
to write exactly N characters from the bytes that str points to. You can write it into the stream using <<too. It will write everything up to the null character, or everything from an std::string, but will respect formatting flags, like the field width:
从 str 指向的字节中准确写入 N 个字符。您也可以使用它将其写入流中<<。它会将所有内容写入空字符或 std::string 中的所有内容，但会尊重格式标志，例如字段宽度：
stream << ptr; // char*
stream << other_str; // everything from std::string
回答by Fredrik Jansson
This will work:
这将起作用：
std::istringstream is("abc...");
And since istringstream is a istream, you will be able to use your is object as an istream.
由于 istringstream 是一个 istream，您将能够将您的 is 对象用作 istream。
