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String Literals

CS253 String Literals

Literals

Literals are constants, like 42, 1.2e-24, 'x', "foo", true, or nullptr.

This is a char: 'X'.
This is a C-style string literal: "alpha beta gamma".
(single quotes for a single character)

C++ 2011 has no std::string literals. C++ 2014 has "foobar"s, with the trailing s, but we won’t discuss those.

String Literals

A "string literal" is an anonymous array of characters. These are equivalent:

cout << "abc123" << '\n';

abc123

const char make_up_a_name[] = "abc123";
cout << make_up_a_name << '\n';

abc123

const char make_up_a_name[] = "abc123";
const char *p = &make_up_a_name[0];
cout << p << '\n';

abc123

• A "string literal" is like an anonymous array.
• An array name is the same as the address of its first element.

Comparing C-Style Strings

if ("beta" < "alpha")   // BAD CODE
    cout << "This is really quite surprising!\n";

c.cc:1: warning: comparison with string literal results in unspecified behavior
This is really quite surprising!

• Look—“unspecified behavior”! Remember that?
• This will not compare the letters in the strings. It will, instead, compare the addresses. Which is at the lower address? Who knows‽
• Are the arrays "marx" and "marx" two arrays or one? Who knows‽
• g++ -Wall will detect this deplorable behavior.

Comparing C-style strings properly.

To compare C-style strings, use the function strcmp. It has a peculiar return value. strcmp(a,b) returns:

• Some value <0 if a<b.
• 0 if a==b.
• Some value >0 if a>b.

Why are you even considering using C-style strings?

Comparing C++ std::strings

To compare C++ std::string values, or to compare a std::string with a C-style string, use the usual operators:

    < > <= >= == !=

Only Java geeks use std::string::compare(), which has the same three-way return value as strcmp.