How to split a string literal across multiple lines in C / Objective-C?

Question

I have a pretty long sqlite query:

const char *sql_query = "SELECT statuses.word_id FROM lang1_words, statuses WHERE statuses.word_id = lang1_words.word_id ORDER BY lang1_words.word ASC";

How can I break it in a number of lines to make it easier to read? If I do the following:

const char *sql_query = "SELECT word_id
                        FROM table1, table2
                        WHERE table2.word_id = table1.word_id
                        ORDER BY table1.word ASC";

I am getting an error.

Is there a way to write queries in multiple lines?

Answer 1

There are two ways to split strings over multiple lines:

1. Each string on its own line. Works only with strings:

   • Plain C:

     char *my_string = "Line 1 "
                       "Line 2";
     

   • Objective-C:

     NSString *my_string = @"Line1 "
                            "Line2";    // the second @ is optional
     

2. Using \ - can be used for any expression:

   • Plain C:

     char *my_string = "Line 1 \
                        Line 2";
     

   • Objective-C:

     NSString *my_string = @"Line1 \
                             Line2";
     

---

The first approach is better, because there isn't a lot of whitespace included. For a SQL query however, both are possible.

NOTE: With a #define, you have to add an extra \ to concatenate the two strings:

Plain C:

#define kMyString "Line 1"\
                  "Line 2"

Answer 2

There's a trick you can do with the pre-processor.
It has the potential down sides that it will collapse white-space, and could be confusing for people reading the code.
But, it has the up side that you don't need to escape quote characters inside it.

#define QUOTE(...) #__VA_ARGS__
const char *sql_query = QUOTE(
    SELECT word_id
    FROM table1, table2
    WHERE table2.word_id = table1.word_id
    ORDER BY table1.word ASC
);

the preprocessor turns this into:

const char *sql_query = "SELECT word_id FROM table1, table2 WHERE table2.word_id = table1.word_id ORDER BY table1.word ASC";

I've used this trick when I was writing some unit tests that had large literal strings containing JSON. It meant that I didn't have to escape every quote character \".

Answer 3

I am having this problem all the time, so I made a tiny tool to convert text to an escaped multi-line Objective-C string:

http://multilineobjc.herokuapp.com/

Hope this saves you some time.

Answer 4

You could also go into XCode -> Preferences, select the Indentation tab, and turn on Line Wrapping.

That way, you won't have to type anything extra, and it will work for the stuff you already wrote. :-)

One annoying thing though is...

if (you're long on indentation
    && short on windows) {
            then your code will
                end up squished
                     against th
                         e side
                             li
                              k
                              e

                              t
                              h
                              i
                              s
}

Answer 5

Extending the Quote idea for Objective-C:

#define NSStringMultiline(...) [[NSString alloc] initWithCString:#__VA_ARGS__ encoding:NSUTF8StringEncoding]

NSString *sql = NSStringMultiline(
    SELECT name, age
    FROM users
    WHERE loggedin = true
);

Answer 6

One more solution for the pile, change your .m file to .mm so that it becomes Objective-C++ and use C++ raw literals, like this:

const char *sql_query = R"(SELECT word_id
                           FROM table1, table2
                           WHERE table2.word_id = table1.word_id
                           ORDER BY table1.word ASC)";

Raw literals ignore everything until the termination sequence, which in the default case is parenthesis-quote.

If the parenthesis-quote sequence has to appear in the string somewhere, you can easily specify a custom delimiter too, like this:

const char *sql_query = R"T3RM!N8(
                                  SELECT word_id
                                  FROM table1, table2
                                  WHERE table2.word_id = table1.word_id
                                  ORDER BY table1.word ASC
                         )T3RM!N8";

Answer 7

GCC adds C++ multiline raw string literals as a C extension

C++11 has raw string literals as mentioned at: https://stackoverflow.com/a/44337236/895245

However, GCC also adds them as a C extension, you just have to use -std=gnu99 instead of -std=c99. E.g.:

main.c

#include <assert.h>
#include <string.h>

int main(void) {
    assert(strcmp(R"(
a
b
)", "\na\nb\n") == 0);
}

Compile and run:

gcc -o main -pedantic -std=gnu99 -Wall -Wextra main.c
./main

This can be used for example to insert multiline inline assembly into C code: How to write multiline inline assembly code in GCC C++?

Now you just have to lay back, and wait for it to be standardized on C20XY.

C++ was asked at: C++ multiline string literal

Tested on Ubuntu 16.04, GCC 6.4.0, binutils 2.26.1.

Answer 8

You can also do:

NSString * query = @"SELECT * FROM foo "
                   @"WHERE "
                     @"bar = 42 "
                     @"AND baz = datetime() "
                   @"ORDER BY fizbit ASC";

Answer 9

An alternative is to use any tool for removing line breaks. Write your string using any text editor, once you finished, paste your text here and copy it again in xcode.