Hi there, I am using regex_replace for string replacing. I am working with a very large string (about 3M) and need to do the following replacment %R% --> #R# %A% --> #R1# %C% --> #R2# and so on. I am new to regular express and regex. After having read the document, I know how regex works, but still not sure if regex_replace meet my demand 1) I invoke regex_replace several times to replace difference patterns. For a large input string, the operation is very slow. Can I call regex_replace once to do the several replacments. i.e. calling regex_replace( output, begin, end, "%R ,%A ,%C", "#R#, #R1#, #R2#", match_default); for replacing %R% with #R# %A% with #R1# %C% with #R2# 2) According to the document, the output fashion depends on the match_flag_type, for my case, I hope the output string, including both matched and nonmatched part, replace the whole input string. e.g. SourceStr = "xxxx%R%yyy%A%zzz%C%" Apply regex_replace( output_string, SourceStr.begin, SourceStr.end, ... ) We have , output_string = "xxxx#R#yyy#R1#zzz#R2#" rather than #R#, #R1# and #R2# Any reply will be highly appreciated.