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CS253 String Literals

Literals

• Literals are constants, like 42, 1.2e-24, 'x', "foo", true, or nullptr.
  • const variables are not literals. They’re variables that don’t vary.
• This is a char: 'X'.
  • Single quotes for a single character.
• This is a C-style string literal: "alpha beta gamma".
• C++ 2011 has no std::string literals.
• C++ 2014 has "foobar"s, with the trailing s, but we won’t discuss it.

String Literals

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

cout << "FN-2187";

FN-2187

const char whatever[] = "FN-2187";
cout << whatever;

FN-2187

const char whatever[] = "FN-2187";
const char *p = &whatever[0];
cout << p;

FN-2187

• 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 ("foo" < "bar")
    cout << "😢";

c.cc:1: warning: comparison with string literal results in unspecified behavior
😢

• 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 code.

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?
  • Well, sometimes, you have to.

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.
• This language has operator overloading. Be thankful!

Example

string name = "Conan O’Brien";
if (name == "Conan O’Brien")
    cout << "good 1\n";
if (name < "Zulu")
    cout << "good 2\n";
if (name > "Andy Richter")
    cout << "good 3\n";
if (name == name)
    cout << "good 4\n";

good 1
good 2
good 3
good 4

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