C++ 我什么时候应该使用字符串而不是字符串流？
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When should I use string instead of stringstream?
提问by Lucas Lima
When should I use stringstreaminstead of string::append()?
Supposing I'm going to catenate just strings.
我什么时候应该使用stringstream而不是string::append()？假设我将只连接字符串。
stringstream ss;
ss << str1 << "str2" << ...
Write(ss.str());
Or:
或者：
string str;
str.reserve(10000);
str.append(str1);
str.append("str2");
...
Write(str);
Which of them is faster?
他们中谁更快？
采纳答案by Praetorian
I don't know which one will be faster, but if I had to guess I'd say your second example is, especially since you've called the reservemember function to allocate a large space for expansion.
我不知道哪个会更快，但如果我不得不猜测我会说你的第二个例子是，特别是因为你已经调用了reserve成员函数来分配一个大空间进行扩展。
If you're only concatenating strings use string::append(or string::operator+=).
如果您只是连接字符串，请使用string::append(或string::operator+=)。
If you're going to convert numbers to their string representation, as well as format them during conversion, and then append the conversion results together, use stringstreams. I mention the formatting part explicitly because if you do not require formatting C++11 offers std::to_stringwhich can be used to convert numeric types to strings.
如果您要将数字转换为其字符串表示形式，并在转换期间对其进行格式化，然后将转换结果附加在一起，请使用 stringstreams。我明确提到了格式化部分，因为如果您不需要格式化 C++11 提供的std::to_string可用于将数字类型转换为字符串的产品。
回答by anio
string.append is much faster. Especially when you reserve.
string.append 快得多。尤其是当您预订时。
If you are concatenating only strings, I would use string.append. I would only use stringstream when I need to automatically convert non-strings to strings for example:
如果您只连接字符串，我会使用 string.append。我只会在需要自动将非字符串转换为字符串时使用 stringstream，例如：
const int x(42);
stringstream ss;
ss << "My favorite number is: " << x << std::endl;
Here stringstream automatically converts x to a string and appends it. I do not need to call atoi. Stringstream will convert all the basic types automatically for you. It is great for that purpose.
这里 stringstream 自动将 x 转换为字符串并附加它。我不需要打电话给 atoi。Stringstream 将为您自动转换所有基本类型。这非常适合这个目的。
Also if you are only going to be directing data into the stringstream to convert it to a string later. You can use ostringstream which is for output.
此外，如果您只想将数据导入 stringstream 以稍后将其转换为字符串。您可以使用用于输出的 ostringstream 。
I hope that helps.
我希望这有帮助。
