CODEWITHSUNDEEP
c++
Mircea Ispas
Mircea Ispas

Reputation: 20800

C++ string literals

why this code compiles?

std::string a = "test"
"a";

I know that " is ignored inside a string if \ is missing and this:

std::string a = "test""a";

will be the same as "testa" but why it compiles when I have space/tab/end of line inside it?

Upvotes: 1

Views: 656

Answers (5)

Cubbi
Cubbi

Reputation: 47498

Whitespace ("space/tab/end of line", as you put it) between adjacent string literals is also ignored.

Since you want to know if this is standard, the C++ standard says:

2.1[lex.phases]/3

The source file is decomposed into preprocessing tokens (2.4) and sequences of white-space characters

2.1[lex.phases]/6

Adjacent ordinary string literal tokens are concatenated.

And white-space characters are defined in 2.4[lex.pptoken]/2 as

space, horizontal tab, new-line, vertical tab, and form-feed

Also, the example of such concatenation, provided in 2.13.4[lex.string]/3 involves space:

[Example:
"\xA" "B"
contains the two characters ’\xA’ and ’B’ after concatenation

which shows that the meaning of "adjacent tokens" in this case includes "separated by space", and therefore, "separated by a sequence of white-space characters", which includes new-line as well.

Upvotes: 9

Rob Agar
Rob Agar

Reputation: 12469

It's by design so you can have

std::string a = "really"
                "long"
                "string literals"
                "spread over multiple lines";

Upvotes: 2

John K
John K

Reputation: 2180

White space is ignored - the semicolon ends your line.

Upvotes: 1

Lightness Races in Orbit
Lightness Races in Orbit

Reputation: 385405

Because the C++ grammar doesn't care about newlines, tabs or whitespace between tokens (as far as possible).

This is valid in much the same way that:

int a = 3 +
        5 +
        9;

is valid.

(Of course you often need some whitespace between tokens to set them apart, e.g. int a; rather than inta;. But as long as the distinction isn't required, the whitespace does not matter, e.g. 3 + 5 or 3+5.)

Upvotes: 4

Daniel A. White
Daniel A. White

Reputation: 191058

The compiler is smart enough to optimize this for you.

C++ ignores end of lines in statements - the semicolon determines when the statement is complete.

Upvotes: 1

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