I can't figure out std::string substr

my font filename extractor is not working... filename_: ".\\Source\\AlexBrush-Regular.ttf" and I'm using

sprintf(buffer, "\nFont Name:%s \nNumber of errors: %d\nAscent %d High +%d Descent -%d Low -%d!", 
                font->filename_.substr( font->filename_.find_last_of('\\'), font->filename_.length() ), hitcount, Ascent, Descent, High, Low);

my ouput looks like buffer 0x008aecbc "\nFont Name:ÀëŠ \nNumber of errors: 12688232\nAscent -858993460 High +-858993460 Descent --858993460 Low -22!"