考虑:
std::string s_a, s_b;
std::stringstream ss_1, ss_2;
// at this stage:
// ss_1 and ss_2 have been used and are now in some strange state
// s_a and s_b contain non-white space words
ss_1.str( std::string() );
ss_1.clear();
ss_1 << s_a;
ss_1 << s_b;
// ss_1.str().c_str() is now the concatenation of s_a and s_b,
// <strike>with</strike> without space between them
ss_2.str( s_a );
ss_2.clear();
// ss_2.str().c_str() is now s_a
ss_2 << s_b; // line ***
// ss_2.str().c_str() the value of s_a is over-written by s_b
//
// Replacing line *** above with "ss_2 << ss_2.str() << " " << s_b;"
// results in ss_2 having the same content as ss_1.
问题:
stringstream.str(a_value); 有什么区别?和 stringstream << a_value; 并且,具体来说,为什么第一个不允许通过 << 进行连接,但第二个允许?
为什么 ss_1 会自动获得 s_a 和 s_b 之间的空白,但是我们是否需要在可以替换行 ***: 的行中显式添加空白ss_2 << ss_2.str() << " " << s_b;
?