linux - how to replace a string in an efficient way in C -

i have string generated linux uuid generation code (libc):

1b4e28ba-2fa1-11d2-883f-b9a761bde3fb

i need replace of characters in string:

- _
2 f
4 x

i generating 200 uuids using loop.

so every uuid need replace using custom function, function must maximum optimised so, how can attain that?

i suppose you're using char[] str

char *c; for(c = str; *c != '\0'; ++c){     if( *c == '-' ) *c = '_';     else if( *c == '2' ) *c = 'f';     else if( *c == '4' ) *c = 'x'; } 

switch version

char *c; for(c = str; *c != '\0'; ++c){     switch(*c){         case '-': *c = '_'; break;         case '2': *c = 'f'; break;         case '4': *c = 'x'; break;     } }