Why doesn't Clang like the __DATE__ macro?

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I use the __DATE__ macro for getting a compile-time year:

const QString build_year = __DATE__ + 7;

The Clang Code Model in QtCreator throws a -Wdate-time warning for using the __DATE__ macro.

warning: expansion of date or time macro is not reproducible

I can disable this warning with -Wno-date-time, but what is wrong with using __DATE__?

What is an "expansion" of the macro, how can it be "reproducible" or "not reproducible", and why is "not reproducible" bad?

c++ clang qt-creator

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edited 9 mins ago

Boann

36k1286116

asked 1 hour ago

yalov

12718

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  The builds are going to be different depending on when you build it (because the date is different).
  – CoffeeTableEspresso
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  I don't believe clang++ enables -Wdate-time by default (I just tried it on my system and I don't get the warning unless I enable it explicitly). Does QtCreator enable it for you? Or make a Makefile or equivalent? You shouldn't get that warning unless something asks for it.
  – Keith Thompson
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  @KeithThompson default clang scheme in the QTCreator is "Clang-only checks for almost everything" - -Weverything -Wno-c++98-compat -Wno-c++98-compat-pedantic -Wno-unused-macros -Wno-newline-eof -Wno-exit-time-destructors -Wno-global-constructors -Wno-gnu-zero-variadic-macro-arguments -Wno-documentation -Wno-shadow -Wno-switch-enum -Wno-missing-prototypes -Wno-used-but-marked-unused
  – yalov
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  @yalov: It's the -Weverything that enables -Wdate-time.
  – Keith Thompson
  1 hour ago
  

  
  
  
  

add a comment | 

up vote
6
down vote

favorite

I use the __DATE__ macro for getting a compile-time year:

const QString build_year = __DATE__ + 7;

The Clang Code Model in QtCreator throws a -Wdate-time warning for using the __DATE__ macro.

warning: expansion of date or time macro is not reproducible

I can disable this warning with -Wno-date-time, but what is wrong with using __DATE__?

What is an "expansion" of the macro, how can it be "reproducible" or "not reproducible", and why is "not reproducible" bad?

c++ clang qt-creator

share|improve this question

edited 9 mins ago

Boann

36k1286116

asked 1 hour ago

yalov

12718

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  The builds are going to be different depending on when you build it (because the date is different).
  – CoffeeTableEspresso
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  I don't believe clang++ enables -Wdate-time by default (I just tried it on my system and I don't get the warning unless I enable it explicitly). Does QtCreator enable it for you? Or make a Makefile or equivalent? You shouldn't get that warning unless something asks for it.
  – Keith Thompson
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  @KeithThompson default clang scheme in the QTCreator is "Clang-only checks for almost everything" - -Weverything -Wno-c++98-compat -Wno-c++98-compat-pedantic -Wno-unused-macros -Wno-newline-eof -Wno-exit-time-destructors -Wno-global-constructors -Wno-gnu-zero-variadic-macro-arguments -Wno-documentation -Wno-shadow -Wno-switch-enum -Wno-missing-prototypes -Wno-used-but-marked-unused
  – yalov
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  @yalov: It's the -Weverything that enables -Wdate-time.
  – Keith Thompson
  1 hour ago
  

  
  
  
  

add a comment | 

up vote
6
down vote

favorite

up vote
6
down vote

favorite

I use the __DATE__ macro for getting a compile-time year:

const QString build_year = __DATE__ + 7;

The Clang Code Model in QtCreator throws a -Wdate-time warning for using the __DATE__ macro.

warning: expansion of date or time macro is not reproducible

I can disable this warning with -Wno-date-time, but what is wrong with using __DATE__?

What is an "expansion" of the macro, how can it be "reproducible" or "not reproducible", and why is "not reproducible" bad?

c++ clang qt-creator

share|improve this question

edited 9 mins ago

Boann

36k1286116

asked 1 hour ago

yalov

12718

I use the __DATE__ macro for getting a compile-time year:

const QString build_year = __DATE__ + 7;

The Clang Code Model in QtCreator throws a -Wdate-time warning for using the __DATE__ macro.

warning: expansion of date or time macro is not reproducible

I can disable this warning with -Wno-date-time, but what is wrong with using __DATE__?

What is an "expansion" of the macro, how can it be "reproducible" or "not reproducible", and why is "not reproducible" bad?

c++ clang qt-creator

c++ clang qt-creator

share|improve this question

edited 9 mins ago

Boann

36k1286116

asked 1 hour ago

yalov

12718

share|improve this question

edited 9 mins ago

Boann

36k1286116

asked 1 hour ago

yalov

12718

share|improve this question

share|improve this question

edited 9 mins ago

Boann

36k1286116

edited 9 mins ago

Boann

36k1286116

edited 9 mins ago

Boann

36k1286116

36k1286116

asked 1 hour ago

yalov

12718

asked 1 hour ago

yalov

12718

asked 1 hour ago

yalov

12718

12718

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  The builds are going to be different depending on when you build it (because the date is different).
  – CoffeeTableEspresso
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  I don't believe clang++ enables -Wdate-time by default (I just tried it on my system and I don't get the warning unless I enable it explicitly). Does QtCreator enable it for you? Or make a Makefile or equivalent? You shouldn't get that warning unless something asks for it.
  – Keith Thompson
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  @KeithThompson default clang scheme in the QTCreator is "Clang-only checks for almost everything" - -Weverything -Wno-c++98-compat -Wno-c++98-compat-pedantic -Wno-unused-macros -Wno-newline-eof -Wno-exit-time-destructors -Wno-global-constructors -Wno-gnu-zero-variadic-macro-arguments -Wno-documentation -Wno-shadow -Wno-switch-enum -Wno-missing-prototypes -Wno-used-but-marked-unused
  – yalov
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  @yalov: It's the -Weverything that enables -Wdate-time.
  – Keith Thompson
  1 hour ago
  

  
  
  
  

add a comment | 

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  The builds are going to be different depending on when you build it (because the date is different).
  – CoffeeTableEspresso
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  I don't believe clang++ enables -Wdate-time by default (I just tried it on my system and I don't get the warning unless I enable it explicitly). Does QtCreator enable it for you? Or make a Makefile or equivalent? You shouldn't get that warning unless something asks for it.
  – Keith Thompson
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  @KeithThompson default clang scheme in the QTCreator is "Clang-only checks for almost everything" - -Weverything -Wno-c++98-compat -Wno-c++98-compat-pedantic -Wno-unused-macros -Wno-newline-eof -Wno-exit-time-destructors -Wno-global-constructors -Wno-gnu-zero-variadic-macro-arguments -Wno-documentation -Wno-shadow -Wno-switch-enum -Wno-missing-prototypes -Wno-used-but-marked-unused
  – yalov
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  @yalov: It's the -Weverything that enables -Wdate-time.
  – Keith Thompson
  1 hour ago
  

  
  
  
  

1

1

The builds are going to be different depending on when you build it (because the date is different).
– CoffeeTableEspresso
1 hour ago

The builds are going to be different depending on when you build it (because the date is different).
– CoffeeTableEspresso
1 hour ago

I don't believe clang++ enables -Wdate-time by default (I just tried it on my system and I don't get the warning unless I enable it explicitly). Does QtCreator enable it for you? Or make a Makefile or equivalent? You shouldn't get that warning unless something asks for it.
– Keith Thompson
1 hour ago

I don't believe clang++ enables -Wdate-time by default (I just tried it on my system and I don't get the warning unless I enable it explicitly). Does QtCreator enable it for you? Or make a Makefile or equivalent? You shouldn't get that warning unless something asks for it.
– Keith Thompson
1 hour ago

1

1

@KeithThompson default clang scheme in the QTCreator is "Clang-only checks for almost everything" - -Weverything -Wno-c++98-compat -Wno-c++98-compat-pedantic -Wno-unused-macros -Wno-newline-eof -Wno-exit-time-destructors -Wno-global-constructors -Wno-gnu-zero-variadic-macro-arguments -Wno-documentation -Wno-shadow -Wno-switch-enum -Wno-missing-prototypes -Wno-used-but-marked-unused
– yalov
1 hour ago

@KeithThompson default clang scheme in the QTCreator is "Clang-only checks for almost everything" - -Weverything -Wno-c++98-compat -Wno-c++98-compat-pedantic -Wno-unused-macros -Wno-newline-eof -Wno-exit-time-destructors -Wno-global-constructors -Wno-gnu-zero-variadic-macro-arguments -Wno-documentation -Wno-shadow -Wno-switch-enum -Wno-missing-prototypes -Wno-used-but-marked-unused
– yalov
1 hour ago

@yalov: It's the -Weverything that enables -Wdate-time.
– Keith Thompson
1 hour ago

@yalov: It's the -Weverything that enables -Wdate-time.
– Keith Thompson
1 hour ago

add a comment | 

2 Answers
2

active

oldest

votes

up vote
9
down vote



accepted

Having repeated builds reproduce binary-identical outputs is desirable from many points of view. Building identical source code from identical tool chains giving different binaries each time could hide serious problems.

If you don't need to produce identical binaries every time you build identical code just disable that warning. that's why the command-line switch exists.

share|improve this answer

answered 1 hour ago

Stephen M. Webb

67927

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  nice concise answer.
  – CoffeeTableEspresso
  1 hour ago
  

  
  
  
  

add a comment | 

up vote
1
down vote

The warning message tells you why. Using the macro does not result in a reproducible build since its value will change over time. A build in 2018 and one in 2019 will not produce the same binary.

share|improve this answer

answered 1 hour ago

Jesper Juhl

14.8k32142

add a comment | 

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2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

active

oldest

votes

active

oldest

votes

up vote
9
down vote



accepted

Having repeated builds reproduce binary-identical outputs is desirable from many points of view. Building identical source code from identical tool chains giving different binaries each time could hide serious problems.

If you don't need to produce identical binaries every time you build identical code just disable that warning. that's why the command-line switch exists.

share|improve this answer

answered 1 hour ago

Stephen M. Webb

67927

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  nice concise answer.
  – CoffeeTableEspresso
  1 hour ago
  

  
  
  
  

add a comment | 

up vote
9
down vote



accepted

Having repeated builds reproduce binary-identical outputs is desirable from many points of view. Building identical source code from identical tool chains giving different binaries each time could hide serious problems.

If you don't need to produce identical binaries every time you build identical code just disable that warning. that's why the command-line switch exists.

share|improve this answer

answered 1 hour ago

Stephen M. Webb

67927

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  nice concise answer.
  – CoffeeTableEspresso
  1 hour ago
  

  
  
  
  

add a comment | 

up vote
9
down vote



accepted

up vote
9
down vote



accepted

Having repeated builds reproduce binary-identical outputs is desirable from many points of view. Building identical source code from identical tool chains giving different binaries each time could hide serious problems.

If you don't need to produce identical binaries every time you build identical code just disable that warning. that's why the command-line switch exists.

share|improve this answer

answered 1 hour ago

Stephen M. Webb

67927

Having repeated builds reproduce binary-identical outputs is desirable from many points of view. Building identical source code from identical tool chains giving different binaries each time could hide serious problems.

If you don't need to produce identical binaries every time you build identical code just disable that warning. that's why the command-line switch exists.

share|improve this answer

answered 1 hour ago

Stephen M. Webb

67927

share|improve this answer

share|improve this answer

answered 1 hour ago

Stephen M. Webb

67927

answered 1 hour ago

Stephen M. Webb

67927

answered 1 hour ago

Stephen M. Webb

67927

67927

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  nice concise answer.
  – CoffeeTableEspresso
  1 hour ago
  

  
  
  
  

add a comment | 

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  nice concise answer.
  – CoffeeTableEspresso
  1 hour ago
  

  
  
  
  

1

1

nice concise answer.
– CoffeeTableEspresso
1 hour ago

nice concise answer.
– CoffeeTableEspresso
1 hour ago

add a comment | 

up vote
1
down vote

The warning message tells you why. Using the macro does not result in a reproducible build since its value will change over time. A build in 2018 and one in 2019 will not produce the same binary.

share|improve this answer

answered 1 hour ago

Jesper Juhl

14.8k32142

add a comment | 

up vote
1
down vote

The warning message tells you why. Using the macro does not result in a reproducible build since its value will change over time. A build in 2018 and one in 2019 will not produce the same binary.

share|improve this answer

answered 1 hour ago

Jesper Juhl

14.8k32142

add a comment | 

up vote
1
down vote

up vote
1
down vote

The warning message tells you why. Using the macro does not result in a reproducible build since its value will change over time. A build in 2018 and one in 2019 will not produce the same binary.

share|improve this answer

answered 1 hour ago

Jesper Juhl

14.8k32142

The warning message tells you why. Using the macro does not result in a reproducible build since its value will change over time. A build in 2018 and one in 2019 will not produce the same binary.

share|improve this answer

answered 1 hour ago

Jesper Juhl

14.8k32142

share|improve this answer

share|improve this answer

answered 1 hour ago

Jesper Juhl

14.8k32142

answered 1 hour ago

Jesper Juhl

14.8k32142

answered 1 hour ago

Jesper Juhl

14.8k32142

14.8k32142

add a comment | 

add a comment | 

 

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