String constants is also know as string literal, it is special type of constants which store fixed sequences characters. String constant is set of characters enclosed double quotes. For example string constant consists of 5 exclamation mark will be '!!!!!' , and empty string or null string will be like "". It occupy two bytes. String constant allow model to be adjusted as strings. String constant size is number of bytes associated with string plus one additional byte for terminating null byte. The character written in double quotes are automatically know as string by the D compiler.