Is it possible to make macros that are default arguments expand at call site?

#include <stdio.h>



void print(int a = __LINE__){printf("hello %dn", a);}



void main(){

  print();

  print();

  print();

  print();

}

The __LINE__ macro in this case expands to 3, so the print function is called 4 times with the same value. Is there a way to convince the compiler to expand this macro at the callsite, so that the print function would be called with 6,7,8,9 instead of 3,3,3,3 with features that exist in C++11?

My usecase:

In my application, I provide multiple functions that take a unique ID. The ID should be unique per callsite/location (so if the function is called two times throught the same statement, it should receive the same id). Currently, the user always has to manually type a LOCATION macro at the callsite, like this:

#define S1(x) #x //voodoo to concat __FILE__ and __LINE__

#define S2(x) S1(x)

#define LOCATION __FILE__ S2(__LINE__)



do_stuff1(arguments, LOCATION)

do_stuff2(arguments, LOCATION)

It would be more convenient if I could save them the typing, without creating a macro for each function like this:

#define do_stuff1(do_stuff1_imp(arguments, LOCATION))

#define do_stuff2(do_stuff2_imp(arguments, LOCATION))

Hence I thought a default argument would do the trick. Is there any way to achieve this?

edited Nov 20 '18 at 18:27

Justin

13.5k95597

asked Nov 20 '18 at 18:13

pulp_user

465

3

Do the work in a macro, #define print() {printf("hello %dn", __LINE__);}.

– Eljay
Nov 20 '18 at 18:16

This is exactly what I wrote in the last code block, only translated on do_stuff instead of print. I am aware of this solution and wanted to know if there was a less tedious way to do this (I have quite a lot of these functions. I would need to make a macro for each of them).

– pulp_user
Nov 20 '18 at 18:19

Wait, no, sorry I was wrong. Your way makes the whole function a macro. That is indeed different. I will consider that, thanks!

– pulp_user
Nov 20 '18 at 18:22

1

@MatthieuBrucher Don't change the tags from C++ to C like that. Even if all of the code in the question would compile with a C compiler, that doesn't make the question a C question (note that default arguments are a C++ feature). The OP is using a C++ compiler and is looking for C++ answers, not C.

– Justin
Nov 20 '18 at 18:28

add a comment |

#include <stdio.h>



void print(int a = __LINE__){printf("hello %dn", a);}



void main(){

  print();

  print();

  print();

  print();

}

My usecase:

#define S1(x) #x //voodoo to concat __FILE__ and __LINE__

#define S2(x) S1(x)

#define LOCATION __FILE__ S2(__LINE__)



do_stuff1(arguments, LOCATION)

do_stuff2(arguments, LOCATION)

It would be more convenient if I could save them the typing, without creating a macro for each function like this:

#define do_stuff1(do_stuff1_imp(arguments, LOCATION))

#define do_stuff2(do_stuff2_imp(arguments, LOCATION))

Hence I thought a default argument would do the trick. Is there any way to achieve this?

edited Nov 20 '18 at 18:27

Justin

13.5k95597

asked Nov 20 '18 at 18:13

pulp_user

465

3

Do the work in a macro, #define print() {printf("hello %dn", __LINE__);}.

– Eljay
Nov 20 '18 at 18:16

This is exactly what I wrote in the last code block, only translated on do_stuff instead of print. I am aware of this solution and wanted to know if there was a less tedious way to do this (I have quite a lot of these functions. I would need to make a macro for each of them).

– pulp_user
Nov 20 '18 at 18:19

Wait, no, sorry I was wrong. Your way makes the whole function a macro. That is indeed different. I will consider that, thanks!

– pulp_user
Nov 20 '18 at 18:22

1

@MatthieuBrucher Don't change the tags from C++ to C like that. Even if all of the code in the question would compile with a C compiler, that doesn't make the question a C question (note that default arguments are a C++ feature). The OP is using a C++ compiler and is looking for C++ answers, not C.

– Justin
Nov 20 '18 at 18:28

add a comment |

#include <stdio.h>



void print(int a = __LINE__){printf("hello %dn", a);}



void main(){

  print();

  print();

  print();

  print();

}

My usecase:

#define S1(x) #x //voodoo to concat __FILE__ and __LINE__

#define S2(x) S1(x)

#define LOCATION __FILE__ S2(__LINE__)



do_stuff1(arguments, LOCATION)

do_stuff2(arguments, LOCATION)

It would be more convenient if I could save them the typing, without creating a macro for each function like this:

#define do_stuff1(do_stuff1_imp(arguments, LOCATION))

#define do_stuff2(do_stuff2_imp(arguments, LOCATION))

Hence I thought a default argument would do the trick. Is there any way to achieve this?

edited Nov 20 '18 at 18:27

Justin

13.5k95597

asked Nov 20 '18 at 18:13

pulp_user

465

#include <stdio.h>



void print(int a = __LINE__){printf("hello %dn", a);}



void main(){

  print();

  print();

  print();

  print();

}

My usecase:

#define S1(x) #x //voodoo to concat __FILE__ and __LINE__

#define S2(x) S1(x)

#define LOCATION __FILE__ S2(__LINE__)



do_stuff1(arguments, LOCATION)

do_stuff2(arguments, LOCATION)

It would be more convenient if I could save them the typing, without creating a macro for each function like this:

#define do_stuff1(do_stuff1_imp(arguments, LOCATION))

#define do_stuff2(do_stuff2_imp(arguments, LOCATION))

Hence I thought a default argument would do the trick. Is there any way to achieve this?

c++ c++11 macros default-arguments

edited Nov 20 '18 at 18:27

Justin

13.5k95597

asked Nov 20 '18 at 18:13

pulp_user

465

edited Nov 20 '18 at 18:27

Justin

13.5k95597

asked Nov 20 '18 at 18:13

pulp_user

465

edited Nov 20 '18 at 18:27

Justin

13.5k95597

edited Nov 20 '18 at 18:27

Justin

13.5k95597

edited Nov 20 '18 at 18:27

Justin

13.5k95597

asked Nov 20 '18 at 18:13

pulp_user

465

asked Nov 20 '18 at 18:13

pulp_user

465

asked Nov 20 '18 at 18:13

pulp_user

465

3

Do the work in a macro, #define print() {printf("hello %dn", __LINE__);}.

– Eljay
Nov 20 '18 at 18:16

This is exactly what I wrote in the last code block, only translated on do_stuff instead of print. I am aware of this solution and wanted to know if there was a less tedious way to do this (I have quite a lot of these functions. I would need to make a macro for each of them).

– pulp_user
Nov 20 '18 at 18:19

Wait, no, sorry I was wrong. Your way makes the whole function a macro. That is indeed different. I will consider that, thanks!

– pulp_user
Nov 20 '18 at 18:22

1

@MatthieuBrucher Don't change the tags from C++ to C like that. Even if all of the code in the question would compile with a C compiler, that doesn't make the question a C question (note that default arguments are a C++ feature). The OP is using a C++ compiler and is looking for C++ answers, not C.

– Justin
Nov 20 '18 at 18:28

add a comment |

3

Do the work in a macro, #define print() {printf("hello %dn", __LINE__);}.

– Eljay
Nov 20 '18 at 18:16

This is exactly what I wrote in the last code block, only translated on do_stuff instead of print. I am aware of this solution and wanted to know if there was a less tedious way to do this (I have quite a lot of these functions. I would need to make a macro for each of them).

– pulp_user
Nov 20 '18 at 18:19

Wait, no, sorry I was wrong. Your way makes the whole function a macro. That is indeed different. I will consider that, thanks!

– pulp_user
Nov 20 '18 at 18:22

1

@MatthieuBrucher Don't change the tags from C++ to C like that. Even if all of the code in the question would compile with a C compiler, that doesn't make the question a C question (note that default arguments are a C++ feature). The OP is using a C++ compiler and is looking for C++ answers, not C.

– Justin
Nov 20 '18 at 18:28

Do the work in a macro, #define print() {printf("hello %dn", __LINE__);}.

– Eljay
Nov 20 '18 at 18:16

This is exactly what I wrote in the last code block, only translated on do_stuff instead of print. I am aware of this solution and wanted to know if there was a less tedious way to do this (I have quite a lot of these functions. I would need to make a macro for each of them).

– pulp_user
Nov 20 '18 at 18:19

Wait, no, sorry I was wrong. Your way makes the whole function a macro. That is indeed different. I will consider that, thanks!

– pulp_user
Nov 20 '18 at 18:22

@MatthieuBrucher Don't change the tags from C++ to C like that. Even if all of the code in the question would compile with a C compiler, that doesn't make the question a C question (note that default arguments are a C++ feature). The OP is using a C++ compiler and is looking for C++ answers, not C.

– Justin
Nov 20 '18 at 18:28

add a comment |

3 Answers
3

active

oldest

votes

The __LINE__ macro in this case expands to 3

Sure because your function declaration is done at line 3 and the prepreprocessor expands it from there.

Another macro instead of a function declaration would do the trick well (taken from @Ejay's comment):

#define print() printf("hello %dn", __LINE__)

See a working example here.

edited Nov 20 '18 at 18:54

Jarod42

115k12101182

answered Nov 20 '18 at 18:21

πάντα ῥεῖ

72.6k974138

@Jarod42 Done that.

– πάντα ῥεῖ
Nov 20 '18 at 18:53

add a comment |

You seem to be looking for std::experimental::source_location, which will be std::source_location in a future standard:

#include <experimental/source_location>



void print(std::experimental::source_location const& location

    = std::experimental::source_location())

{

    printf("hello %s:%dn", location.file_name(), location.line());

}

answered Nov 20 '18 at 18:18

Justin

13.5k95597

1

This is indeed exactly what I was looking for. I will not be able to use C++17 though (which this requires I think?). Sorry, I forgot to mention this in the question. I will keep this in mind for the future though. Thanks!

– pulp_user
Nov 20 '18 at 18:24

1

@pulp_user It doesn't require C++17, it requires that your standard library / compiler implements at least this part of the library fundamentals TS v2. You can try it and see if it works, else look at the documentation for your compiler / standard library to see if it works

– Justin
Nov 20 '18 at 18:25

add a comment |

You can write a macro which inserts the __FILE__ and __LINE__ into the argument list:

// Note: this doesn't work with a 0-argument function. Supporting 0-arg functions

// is much harder to do; I'd recommend just having a separate macro like as follows

#define LOCATED(fn, ...) fn(__VA_ARGS__, __FILE__, __LINE__)



#define LOCATED0(fn) fn(__FILE__, __LINE__)



void print(char const* file_name, int line)

{

    printf("hello %s:%dn", file_name, line);

}



int do_something(int value, char const* file_name, int line);



int main() {

    LOCATED0(print);

    LOCATED(do_something, 42);

}

With a little more work, you can make it look nicer at the call-site:

#define LOCATED(...) LOCATED_##__VA_ARGS__



void print(char const* file_name, int line)

{

    printf("hello %s:%dn", file_name, line);

}

#define LOCATED_print() ::print(__FILE__, __LINE__)



int do_something(int value, char const* file_name, int line);

#define LOCATED_do_something(value) ::do_something(value, __FILE__, __LINE__)



int main() {

    LOCATED(print());

    LOCATED(do_something(42));

}

edited Nov 20 '18 at 18:45

answered Nov 20 '18 at 18:36

Justin

13.5k95597

I fail to see how this is different from print(LOCATION) (how I currently do it in my code) besides turning it inside out.

– pulp_user
Nov 20 '18 at 18:40

1

@pulp_user You are right that it's not better than print(LOCATION), but it's an alternative

– Justin
Nov 20 '18 at 18:48

add a comment |

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3 Answers
3

active

oldest

votes

3 Answers
3

active

oldest

votes

The __LINE__ macro in this case expands to 3

Sure because your function declaration is done at line 3 and the prepreprocessor expands it from there.

Another macro instead of a function declaration would do the trick well (taken from @Ejay's comment):

#define print() printf("hello %dn", __LINE__)

See a working example here.

edited Nov 20 '18 at 18:54

Jarod42

115k12101182

answered Nov 20 '18 at 18:21

πάντα ῥεῖ

72.6k974138

@Jarod42 Done that.

– πάντα ῥεῖ
Nov 20 '18 at 18:53

add a comment |

The __LINE__ macro in this case expands to 3

Sure because your function declaration is done at line 3 and the prepreprocessor expands it from there.

Another macro instead of a function declaration would do the trick well (taken from @Ejay's comment):

#define print() printf("hello %dn", __LINE__)

See a working example here.

edited Nov 20 '18 at 18:54

Jarod42

115k12101182

answered Nov 20 '18 at 18:21

πάντα ῥεῖ

72.6k974138

@Jarod42 Done that.

– πάντα ῥεῖ
Nov 20 '18 at 18:53

add a comment |

The __LINE__ macro in this case expands to 3

Sure because your function declaration is done at line 3 and the prepreprocessor expands it from there.

Another macro instead of a function declaration would do the trick well (taken from @Ejay's comment):

#define print() printf("hello %dn", __LINE__)

See a working example here.

edited Nov 20 '18 at 18:54

Jarod42

115k12101182

answered Nov 20 '18 at 18:21

πάντα ῥεῖ

72.6k974138

The __LINE__ macro in this case expands to 3

Sure because your function declaration is done at line 3 and the prepreprocessor expands it from there.

Another macro instead of a function declaration would do the trick well (taken from @Ejay's comment):

#define print() printf("hello %dn", __LINE__)

See a working example here.

edited Nov 20 '18 at 18:54

Jarod42

115k12101182

answered Nov 20 '18 at 18:21

πάντα ῥεῖ

72.6k974138

edited Nov 20 '18 at 18:54

Jarod42

115k12101182

edited Nov 20 '18 at 18:54

Jarod42

115k12101182

edited Nov 20 '18 at 18:54

Jarod42

115k12101182

answered Nov 20 '18 at 18:21

πάντα ῥεῖ

72.6k974138

answered Nov 20 '18 at 18:21

πάντα ῥεῖ

72.6k974138

answered Nov 20 '18 at 18:21

πάντα ῥεῖ

72.6k974138

@Jarod42 Done that.

– πάντα ῥεῖ
Nov 20 '18 at 18:53

add a comment |

@Jarod42 Done that.

– πάντα ῥεῖ
Nov 20 '18 at 18:53

@Jarod42 Done that.

– πάντα ῥεῖ
Nov 20 '18 at 18:53

add a comment |

You seem to be looking for std::experimental::source_location, which will be std::source_location in a future standard:

#include <experimental/source_location>



void print(std::experimental::source_location const& location

    = std::experimental::source_location())

{

    printf("hello %s:%dn", location.file_name(), location.line());

}

answered Nov 20 '18 at 18:18

Justin

13.5k95597

1

This is indeed exactly what I was looking for. I will not be able to use C++17 though (which this requires I think?). Sorry, I forgot to mention this in the question. I will keep this in mind for the future though. Thanks!

– pulp_user
Nov 20 '18 at 18:24

1

@pulp_user It doesn't require C++17, it requires that your standard library / compiler implements at least this part of the library fundamentals TS v2. You can try it and see if it works, else look at the documentation for your compiler / standard library to see if it works

– Justin
Nov 20 '18 at 18:25

add a comment |

You seem to be looking for std::experimental::source_location, which will be std::source_location in a future standard:

#include <experimental/source_location>



void print(std::experimental::source_location const& location

    = std::experimental::source_location())

{

    printf("hello %s:%dn", location.file_name(), location.line());

}

answered Nov 20 '18 at 18:18

Justin

13.5k95597

1

This is indeed exactly what I was looking for. I will not be able to use C++17 though (which this requires I think?). Sorry, I forgot to mention this in the question. I will keep this in mind for the future though. Thanks!

– pulp_user
Nov 20 '18 at 18:24

1

@pulp_user It doesn't require C++17, it requires that your standard library / compiler implements at least this part of the library fundamentals TS v2. You can try it and see if it works, else look at the documentation for your compiler / standard library to see if it works

– Justin
Nov 20 '18 at 18:25

add a comment |

You seem to be looking for std::experimental::source_location, which will be std::source_location in a future standard:

#include <experimental/source_location>



void print(std::experimental::source_location const& location

    = std::experimental::source_location())

{

    printf("hello %s:%dn", location.file_name(), location.line());

}

answered Nov 20 '18 at 18:18

Justin

13.5k95597

You seem to be looking for std::experimental::source_location, which will be std::source_location in a future standard:

#include <experimental/source_location>



void print(std::experimental::source_location const& location

    = std::experimental::source_location())

{

    printf("hello %s:%dn", location.file_name(), location.line());

}

answered Nov 20 '18 at 18:18

Justin

13.5k95597

answered Nov 20 '18 at 18:18

Justin

13.5k95597

answered Nov 20 '18 at 18:18

Justin

13.5k95597

answered Nov 20 '18 at 18:18

Justin

13.5k95597

1

This is indeed exactly what I was looking for. I will not be able to use C++17 though (which this requires I think?). Sorry, I forgot to mention this in the question. I will keep this in mind for the future though. Thanks!

– pulp_user
Nov 20 '18 at 18:24

1

@pulp_user It doesn't require C++17, it requires that your standard library / compiler implements at least this part of the library fundamentals TS v2. You can try it and see if it works, else look at the documentation for your compiler / standard library to see if it works

– Justin
Nov 20 '18 at 18:25

add a comment |

1

This is indeed exactly what I was looking for. I will not be able to use C++17 though (which this requires I think?). Sorry, I forgot to mention this in the question. I will keep this in mind for the future though. Thanks!

– pulp_user
Nov 20 '18 at 18:24

1

@pulp_user It doesn't require C++17, it requires that your standard library / compiler implements at least this part of the library fundamentals TS v2. You can try it and see if it works, else look at the documentation for your compiler / standard library to see if it works

– Justin
Nov 20 '18 at 18:25

This is indeed exactly what I was looking for. I will not be able to use C++17 though (which this requires I think?). Sorry, I forgot to mention this in the question. I will keep this in mind for the future though. Thanks!

– pulp_user
Nov 20 '18 at 18:24

@pulp_user It doesn't require C++17, it requires that your standard library / compiler implements at least this part of the library fundamentals TS v2. You can try it and see if it works, else look at the documentation for your compiler / standard library to see if it works

– Justin
Nov 20 '18 at 18:25

add a comment |

You can write a macro which inserts the __FILE__ and __LINE__ into the argument list:

// Note: this doesn't work with a 0-argument function. Supporting 0-arg functions

// is much harder to do; I'd recommend just having a separate macro like as follows

#define LOCATED(fn, ...) fn(__VA_ARGS__, __FILE__, __LINE__)



#define LOCATED0(fn) fn(__FILE__, __LINE__)



void print(char const* file_name, int line)

{

    printf("hello %s:%dn", file_name, line);

}



int do_something(int value, char const* file_name, int line);



int main() {

    LOCATED0(print);

    LOCATED(do_something, 42);

}

With a little more work, you can make it look nicer at the call-site:

#define LOCATED(...) LOCATED_##__VA_ARGS__



void print(char const* file_name, int line)

{

    printf("hello %s:%dn", file_name, line);

}

#define LOCATED_print() ::print(__FILE__, __LINE__)



int do_something(int value, char const* file_name, int line);

#define LOCATED_do_something(value) ::do_something(value, __FILE__, __LINE__)



int main() {

    LOCATED(print());

    LOCATED(do_something(42));

}

edited Nov 20 '18 at 18:45

answered Nov 20 '18 at 18:36

Justin

13.5k95597

I fail to see how this is different from print(LOCATION) (how I currently do it in my code) besides turning it inside out.

– pulp_user
Nov 20 '18 at 18:40

1

@pulp_user You are right that it's not better than print(LOCATION), but it's an alternative

– Justin
Nov 20 '18 at 18:48

add a comment |

You can write a macro which inserts the __FILE__ and __LINE__ into the argument list:

// Note: this doesn't work with a 0-argument function. Supporting 0-arg functions

// is much harder to do; I'd recommend just having a separate macro like as follows

#define LOCATED(fn, ...) fn(__VA_ARGS__, __FILE__, __LINE__)



#define LOCATED0(fn) fn(__FILE__, __LINE__)



void print(char const* file_name, int line)

{

    printf("hello %s:%dn", file_name, line);

}



int do_something(int value, char const* file_name, int line);



int main() {

    LOCATED0(print);

    LOCATED(do_something, 42);

}

With a little more work, you can make it look nicer at the call-site:

#define LOCATED(...) LOCATED_##__VA_ARGS__



void print(char const* file_name, int line)

{

    printf("hello %s:%dn", file_name, line);

}

#define LOCATED_print() ::print(__FILE__, __LINE__)



int do_something(int value, char const* file_name, int line);

#define LOCATED_do_something(value) ::do_something(value, __FILE__, __LINE__)



int main() {

    LOCATED(print());

    LOCATED(do_something(42));

}

edited Nov 20 '18 at 18:45

answered Nov 20 '18 at 18:36

Justin

13.5k95597

I fail to see how this is different from print(LOCATION) (how I currently do it in my code) besides turning it inside out.

– pulp_user
Nov 20 '18 at 18:40

1

@pulp_user You are right that it's not better than print(LOCATION), but it's an alternative

– Justin
Nov 20 '18 at 18:48

add a comment |

You can write a macro which inserts the __FILE__ and __LINE__ into the argument list:

// Note: this doesn't work with a 0-argument function. Supporting 0-arg functions

// is much harder to do; I'd recommend just having a separate macro like as follows

#define LOCATED(fn, ...) fn(__VA_ARGS__, __FILE__, __LINE__)



#define LOCATED0(fn) fn(__FILE__, __LINE__)



void print(char const* file_name, int line)

{

    printf("hello %s:%dn", file_name, line);

}



int do_something(int value, char const* file_name, int line);



int main() {

    LOCATED0(print);

    LOCATED(do_something, 42);

}

With a little more work, you can make it look nicer at the call-site:

#define LOCATED(...) LOCATED_##__VA_ARGS__



void print(char const* file_name, int line)

{

    printf("hello %s:%dn", file_name, line);

}

#define LOCATED_print() ::print(__FILE__, __LINE__)



int do_something(int value, char const* file_name, int line);

#define LOCATED_do_something(value) ::do_something(value, __FILE__, __LINE__)



int main() {

    LOCATED(print());

    LOCATED(do_something(42));

}

edited Nov 20 '18 at 18:45

answered Nov 20 '18 at 18:36

Justin

13.5k95597

You can write a macro which inserts the __FILE__ and __LINE__ into the argument list:

// Note: this doesn't work with a 0-argument function. Supporting 0-arg functions

// is much harder to do; I'd recommend just having a separate macro like as follows

#define LOCATED(fn, ...) fn(__VA_ARGS__, __FILE__, __LINE__)



#define LOCATED0(fn) fn(__FILE__, __LINE__)



void print(char const* file_name, int line)

{

    printf("hello %s:%dn", file_name, line);

}



int do_something(int value, char const* file_name, int line);



int main() {

    LOCATED0(print);

    LOCATED(do_something, 42);

}

With a little more work, you can make it look nicer at the call-site:

#define LOCATED(...) LOCATED_##__VA_ARGS__



void print(char const* file_name, int line)

{

    printf("hello %s:%dn", file_name, line);

}

#define LOCATED_print() ::print(__FILE__, __LINE__)



int do_something(int value, char const* file_name, int line);

#define LOCATED_do_something(value) ::do_something(value, __FILE__, __LINE__)



int main() {

    LOCATED(print());

    LOCATED(do_something(42));

}

edited Nov 20 '18 at 18:45

answered Nov 20 '18 at 18:36

Justin

13.5k95597

edited Nov 20 '18 at 18:45

answered Nov 20 '18 at 18:36

Justin

13.5k95597

answered Nov 20 '18 at 18:36

Justin

13.5k95597

answered Nov 20 '18 at 18:36

Justin

13.5k95597

I fail to see how this is different from print(LOCATION) (how I currently do it in my code) besides turning it inside out.

– pulp_user
Nov 20 '18 at 18:40

1

@pulp_user You are right that it's not better than print(LOCATION), but it's an alternative

– Justin
Nov 20 '18 at 18:48

add a comment |

I fail to see how this is different from print(LOCATION) (how I currently do it in my code) besides turning it inside out.

– pulp_user
Nov 20 '18 at 18:40

1

@pulp_user You are right that it's not better than print(LOCATION), but it's an alternative

– Justin
Nov 20 '18 at 18:48

I fail to see how this is different from print(LOCATION) (how I currently do it in my code) besides turning it inside out.

– pulp_user
Nov 20 '18 at 18:40

@pulp_user You are right that it's not better than print(LOCATION), but it's an alternative

– Justin
Nov 20 '18 at 18:48

add a comment |

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