#define string over multiple lines [closed]

Question

I was wondering how I could define a really long string over the multiple lines. I tried so many different patterns, but none of them is working.. Here is my code.

#define EXAMPLE "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
                "bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"
                "ccccccccccccccccccccccccccccccccccc"
                "ddddddddddddddddddddddddddddddddddd"

and I get syntax error. The error I got is

ccompile.h (as included in test.c)
=================
error: syntax error before or at: g
*** Error code 2

I want to assign "aaaaaaaaaaaaaaaaaaaaabbbbbbbbbbbbbbbbbbccccccccccccccdddddddd" to EXAMPLE.

I tried using \ and @\ but that didn't work out.

Answer 1

Just get rid of the whitespace in between the lines, and quote the whole thing. A \ at the EOL basically "escapes" the newline, so it won't be part of the string itself. It's only relevant for the preprocessor:

#include <stdio.h>

#define LONG_STRING "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\
bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\
ccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc"

int main ( void ) {
    printf(LONG_STRING);
    return 0;
}

That works just fine

For aesthetic reasons, you can quote each line separately, the only requirement is you add the \ directly after the closing quotes:

#define LONG_STRING "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"\
                    "bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"\
                    "ccccccccccccccccccccccccccccccccccccccccccccc"

This, too, works just fine

Note:

The two suggestions are not 100% equivalent. The first version defines a macro to be a single string literal. The second version defines the macro as 3 separate string literals. For the most part, this isn't a big deal, because during the translation phase, adjacent string literal tokens should be concatenated:

5.1.1.2 Translation phases:
[...]
6. Adjacent string literal tokens are concatenated.
7. White-space characters separating tokens are no longer significant. Each preprocessing token is converted into a token. The resulting tokens are syntactically and semantically analyzed and translated as a translation unit.

I could not find the footnote Meninx mentions about C99 behaving differently. Document I used can be found here

Answer 2

#define EXAMPLE "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
                "bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"
                "ccccccccccccccccccccccccccccccccccc"
                "ddddddddddddddddddddddddddddddddddd"

For the directive above, its replacement list is limited only to "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" because macro definition works only a single logical line.

Moreover, concatenating adjacent string literals to form a single one is not possible in C during preprocessing.

C99 footnote 148:

_{148: Note that adjacent string literals are not concatenated into a single string literal}

Instead use the backslash-newline :

#define EXAMPLE "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\
bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb\
ccccccccccccccccccccccccccccccccccc\
ddddddddddddddddddddddddddddddddddd"

C99 5.1.1.2 p/2

2. Each instance of a backslash character () immediately followed by a new-line character is deleted, splicing physical source lines to form logical source lines. Only the last backslash on any physical source line shall be eligible for being part of such a splice. A source file that is not empty shall end in a new-line character, which shall not be immediately preceded by a backslash character before any such splicing takes place.