[英]How to insert a string to the beginning of a stringstream
For example only and not the actual code: 仅作为示例而非实际代码:
stringstream ss;
ss << " world!";
string hello("Hello");
// insert hello to beginning of ss ??
Thanks for all the responses, I also found this code, which works: 感谢所有答复,我也找到了下面的代码,该代码可以正常工作:
ostringstream& insert( ostringstream& oss, const string& s )
{
streamsize pos = oss.tellp();
oss.str( s + oss.str() );
oss.seekp( pos + s.length() );
return oss;
}
You cannot do it without making at least one copy. 不复制至少一份就无法做到。 One way:
单程:
std::stringstream ss;
ss << " world!";
const std::string &temp = ss.str();
ss.seekp(0);
ss << "Hello";
ss << temp;
This relies on the "most important const
" to extend the lifetime of the temporary and avoid making an extra copy. 这依赖于“最重要的
const
”来延长临时文件的生存期,并避免制作额外的副本。
Or, simpler and possibly faster: 或者,更简单甚至更快:
std::stringstream ss;
ss << " world!";
std::stringstream temp;
temp << "Hello";
temp << ss.rdbuf();
ss = std::move(temp); // or ss.swap(temp);
This borrows the rdbuf
approach from this answer , since the interesting problem here is how to minimize copies. 这是从这个答案中借用
rdbuf
方法的,因为这里有趣的问题是如何最小化副本。
the only way i can see is to create the string from stream and prefix your other string 我看到的唯一方法是从流中创建字符串并为其他字符串添加前缀
string result = hello + ss.str();
its called a stream for a reason. 它之所以称为流是有原因的。
Assuming ss1 contains "hello" 假设ss1包含“ hello”
ss1 << ss.rdbuf();
or 要么
ss1 << "hello" << ss;
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