c++ - Add char to a std::string -

i append char std::string in c++. can think of @ least 3 ways it:

std::string s = "hello"; char c = '!';  s += c; s.append(c); s.push_back(c); 

• which 1 considered best practice ?
• is there performance difference (c++11) ?

also, if want add 2 strings, same question with:

std::string s1 = "hello ", s2 = "world";  s1.append(s2); s1 += s2; 

the question matter of compiler , personal taste and/or company coding style requirements. on loaded operator resolves 2nd choice.

i go first 1 myself