Wrong token pasting/concatenation when token contains spaces

Stumbled over this issue when i added a define for the Qt macro Q_D(), see Cppcheck ticket https://trac.cppcheck.net/ticket/8479.
For this C code:

#define CONCAT(tok) tok##suffix

CONCAT(Test);
CONCAT(const Test);

gcc outputs:

$ gcc -E token_pasting_with_space.c
# 1 "token_pasting_with_space.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "token_pasting_with_space.c"


Testsuffix;
const Testsuffix;

simplecpp outputs:

$ ./simplecpp token_pasting_with_space.c


Testsuffix ;
constTestsuffix ;

The space between "const" and "Test" is removed.
Not sure what the standard says about such a case but since Qt and gcc are widely used i guess it should work like Qt expects it and gcc handles it to not break things.

qt.cfg: Add macro Q_DECLARE_PRIVATE (disabled for now)

Fix token pasting in macro when argument contains spaces. Fixes cppch…

I have the feeling we merge "const Test suffix" into 1 token by intention.

You did not say if gcc preprocessor outputs 1 single token or 2.. you only showed the text output.

I have not found a way to get gcc printing the tokens.
But clang has an option to output tokens:

$ clang test.c -Xclang -dump-tokens
identifier 'Testsuffix'  [StartOfLine]  Loc=<test.c:3:1 <Spelling=<scratch space>:2:1>>
semi ';'                Loc=<test.c:3:13>
const 'const'    [StartOfLine]  Loc=<test.c:4:1 <Spelling=test.c:4:8>>
identifier 'Testsuffix'  [LeadingSpace] Loc=<test.c:4:1 <Spelling=<scratch space>:3:1>>
semi ';'                Loc=<test.c:4:19>
eof ''          Loc=<test.c:4:20>

clang seems to see two tokens.

Nice! ok I agree we need to output 2 separate tokens. Well.. I still have the feeling we merge them by intention.

I did not see any hashhash test that required merging. Only a hash test. So maybe it won't break anything to fix this.

@danmar

This has been tested with ad9b49d and prints now the expected result:

$ ./simplecpp test.c


Testsuffix ;
const Testsuffix ;

@danmar Do you have a test case in place already?

1:
2: 
3: Testsuffix ;
4: const Testsuffix ;

test.cpp: added test for cppcheck-opensource#124 [skip ci]

test.cpp: added test for cppcheck-opensource#124

test.cpp: added tests for cppcheck-opensource#40

test.cpp: added test for cppcheck-opensource#124

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Wrong token pasting/concatenation when token contains spaces #124

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Wrong token pasting/concatenation when token contains spaces #124

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danmar commented on Aug 3, 2019

versat commented on Aug 3, 2019

danmar commented on Aug 4, 2019

danmar commented on Aug 4, 2019

orbitcowboy commented on Mar 18, 2024

firewave commented on Jul 3, 2025

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