Variables C macro function
What's happening in this macro? I understand that #test expand this parameter to the literal text. But what does pre; and test; do?
#define MACRO_FN(test, pre, repeat, size)
do {
printf("%s: ", #test);
for (int i = 0; i < repeat; i++) {
pre;
test;
}
} while (0)
This is used like so
MACRO_FN(a_func(an_array, size),, var1, size);
What do the double commas mean here?
c macros c-preprocessor
asked Nov 19 '18 at 12:34
Jack EvansJack Evans
385
|
show 5 more comments
What's happening in this macro? I understand that #test expand this parameter to the literal text. But what does pre; and test; do?
#define MACRO_FN(test, pre, repeat, size)
do {
printf("%s: ", #test);
for (int i = 0; i < repeat; i++) {
pre;
test;
}
} while (0)
This is used like so
MACRO_FN(a_func(an_array, size),, var1, size);
What do the double commas mean here?
c macros c-preprocessor
asked Nov 19 '18 at 12:34
Jack EvansJack Evans
385
3
Run the code through the preprocessor and look what the macro expands to.
– Some programmer dude
Nov 19 '18 at 12:36
1
To omitpre;- maybe? Did you check the pre-processed code?
– Sourav Ghosh
Nov 19 '18 at 12:37
I didn't think to check the output of the pre-processor, but I'll do that now
– Jack Evans
Nov 19 '18 at 12:47
2
When invoking a preprocessor macro , "blank" is a valid argument; the callMACRO_FN(a,,b,c)means thatprewill expand to blank
– M.M
Nov 19 '18 at 12:50
2
Please note that macros like these should be avoided like the plague.
– Lundin
Nov 19 '18 at 12:55
|
show 5 more comments
What's happening in this macro? I understand that #test expand this parameter to the literal text. But what does pre; and test; do?
#define MACRO_FN(test, pre, repeat, size)
do {
printf("%s: ", #test);
for (int i = 0; i < repeat; i++) {
pre;
test;
}
} while (0)
This is used like so
MACRO_FN(a_func(an_array, size),, var1, size);
What do the double commas mean here?
c macros c-preprocessor
asked Nov 19 '18 at 12:34
Jack EvansJack Evans
385
What's happening in this macro? I understand that #test expand this parameter to the literal text. But what does pre; and test; do?
#define MACRO_FN(test, pre, repeat, size)
do {
printf("%s: ", #test);
for (int i = 0; i < repeat; i++) {
pre;
test;
}
} while (0)
This is used like so
MACRO_FN(a_func(an_array, size),, var1, size);
What do the double commas mean here?
c macros c-preprocessor
c macros c-preprocessor
asked Nov 19 '18 at 12:34
Jack EvansJack Evans
385
asked Nov 19 '18 at 12:34
Jack EvansJack Evans
385
edited Nov 19 '18 at 14:15
Jack Evans
asked Nov 19 '18 at 12:34
Jack EvansJack Evans
385
asked Nov 19 '18 at 12:34
Jack EvansJack Evans
385
asked Nov 19 '18 at 12:34
Jack EvansJack Evans
385
385
3
Run the code through the preprocessor and look what the macro expands to.
– Some programmer dude
Nov 19 '18 at 12:36
1
To omitpre;- maybe? Did you check the pre-processed code?
– Sourav Ghosh
Nov 19 '18 at 12:37
I didn't think to check the output of the pre-processor, but I'll do that now
– Jack Evans
Nov 19 '18 at 12:47
2
When invoking a preprocessor macro , "blank" is a valid argument; the callMACRO_FN(a,,b,c)means thatprewill expand to blank
– M.M
Nov 19 '18 at 12:50
2
Please note that macros like these should be avoided like the plague.
– Lundin
Nov 19 '18 at 12:55
|
show 5 more comments
3
Run the code through the preprocessor and look what the macro expands to.
– Some programmer dude
Nov 19 '18 at 12:36
1
To omitpre;- maybe? Did you check the pre-processed code?
– Sourav Ghosh
Nov 19 '18 at 12:37
I didn't think to check the output of the pre-processor, but I'll do that now
– Jack Evans
Nov 19 '18 at 12:47
2
When invoking a preprocessor macro , "blank" is a valid argument; the callMACRO_FN(a,,b,c)means thatprewill expand to blank
– M.M
Nov 19 '18 at 12:50
2
Please note that macros like these should be avoided like the plague.
– Lundin
Nov 19 '18 at 12:55
3
3
Run the code through the preprocessor and look what the macro expands to.
– Some programmer dude
Nov 19 '18 at 12:36
Run the code through the preprocessor and look what the macro expands to.
– Some programmer dude
Nov 19 '18 at 12:36
1
1
To omit
pre;- maybe? Did you check the pre-processed code?– Sourav Ghosh
Nov 19 '18 at 12:37
To omit
pre;- maybe? Did you check the pre-processed code?– Sourav Ghosh
Nov 19 '18 at 12:37
I didn't think to check the output of the pre-processor, but I'll do that now
– Jack Evans
Nov 19 '18 at 12:47
I didn't think to check the output of the pre-processor, but I'll do that now
– Jack Evans
Nov 19 '18 at 12:47
2
2
When invoking a preprocessor macro , "blank" is a valid argument; the call
MACRO_FN(a,,b,c) means that pre will expand to blank– M.M
Nov 19 '18 at 12:50
When invoking a preprocessor macro , "blank" is a valid argument; the call
MACRO_FN(a,,b,c) means that pre will expand to blank– M.M
Nov 19 '18 at 12:50
2
2
Please note that macros like these should be avoided like the plague.
– Lundin
Nov 19 '18 at 12:55
Please note that macros like these should be avoided like the plague.
– Lundin
Nov 19 '18 at 12:55
|
show 5 more comments
2 Answers
2
active
oldest
votes
Here is a minimal example:
#define repeat 5 // I added this, because 'repeat' is not mentionned in your question
#define MACRO_FN(test, pre, var1, size)
do {
printf("%s: ", #test);
for (int i = 0; i < repeat; i++) {
pre;
test;
}
} while (0)
void foo()
{
}
void func(int a, int b)
{
}
int main()
{
MACRO_FN(func(2, 3), foo(), var1, size);
}
Once preprocessed, the code is equivalent to this:
int main()
{
printf("%s: ", "func(2,3)");
for (int i = 0; i < 5; i++)
{
foo();
func(2, 3);
}
}
So that macro is a wrapper that prints the function name plus it's parameters as it is invoked with the macro and executes that function specified in the first parameter repeat times (whatever repeat is). If the second parameter is omitted, the function that has that name is simple not invoked before the function mentioned before as in the following example:
int main()
{
MACRO_FN(func(2, 3),, var1, size);
}
Once preprocessed, the code is equivalent to this:
int main()
{
printf("%s: ", "func(2,3)");
for (int i = 0; i < 5; i++)
{
;
func(2, 3);
}
}
Note:
I removed the do while(0) from the equivalent programs for brevity, read this SO article for more information:
answered Nov 19 '18 at 14:11
JabberwockyJabberwocky
26.6k93770
add a comment |
pre and test seem to be two functions.
Based on how it is written, we can guess that pre is a function called before the test.
The double comma has no special meaning. It is just here because the second parameter (pre) was omitted.
Edit: As a side note that kind of macro "should be avoided like plague", as @Lundin put it.
answered Nov 19 '18 at 12:42
XaxetrovXaxetrov
544
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
Here is a minimal example:
#define repeat 5 // I added this, because 'repeat' is not mentionned in your question
#define MACRO_FN(test, pre, var1, size)
do {
printf("%s: ", #test);
for (int i = 0; i < repeat; i++) {
pre;
test;
}
} while (0)
void foo()
{
}
void func(int a, int b)
{
}
int main()
{
MACRO_FN(func(2, 3), foo(), var1, size);
}
Once preprocessed, the code is equivalent to this:
int main()
{
printf("%s: ", "func(2,3)");
for (int i = 0; i < 5; i++)
{
foo();
func(2, 3);
}
}
So that macro is a wrapper that prints the function name plus it's parameters as it is invoked with the macro and executes that function specified in the first parameter repeat times (whatever repeat is). If the second parameter is omitted, the function that has that name is simple not invoked before the function mentioned before as in the following example:
int main()
{
MACRO_FN(func(2, 3),, var1, size);
}
Once preprocessed, the code is equivalent to this:
int main()
{
printf("%s: ", "func(2,3)");
for (int i = 0; i < 5; i++)
{
;
func(2, 3);
}
}
Note:
I removed the do while(0) from the equivalent programs for brevity, read this SO article for more information:
answered Nov 19 '18 at 14:11
JabberwockyJabberwocky
26.6k93770
add a comment |
Here is a minimal example:
#define repeat 5 // I added this, because 'repeat' is not mentionned in your question
#define MACRO_FN(test, pre, var1, size)
do {
printf("%s: ", #test);
for (int i = 0; i < repeat; i++) {
pre;
test;
}
} while (0)
void foo()
{
}
void func(int a, int b)
{
}
int main()
{
MACRO_FN(func(2, 3), foo(), var1, size);
}
Once preprocessed, the code is equivalent to this:
int main()
{
printf("%s: ", "func(2,3)");
for (int i = 0; i < 5; i++)
{
foo();
func(2, 3);
}
}
So that macro is a wrapper that prints the function name plus it's parameters as it is invoked with the macro and executes that function specified in the first parameter repeat times (whatever repeat is). If the second parameter is omitted, the function that has that name is simple not invoked before the function mentioned before as in the following example:
int main()
{
MACRO_FN(func(2, 3),, var1, size);
}
Once preprocessed, the code is equivalent to this:
int main()
{
printf("%s: ", "func(2,3)");
for (int i = 0; i < 5; i++)
{
;
func(2, 3);
}
}
Note:
I removed the do while(0) from the equivalent programs for brevity, read this SO article for more information:
answered Nov 19 '18 at 14:11
JabberwockyJabberwocky
26.6k93770
add a comment |
Here is a minimal example:
#define repeat 5 // I added this, because 'repeat' is not mentionned in your question
#define MACRO_FN(test, pre, var1, size)
do {
printf("%s: ", #test);
for (int i = 0; i < repeat; i++) {
pre;
test;
}
} while (0)
void foo()
{
}
void func(int a, int b)
{
}
int main()
{
MACRO_FN(func(2, 3), foo(), var1, size);
}
Once preprocessed, the code is equivalent to this:
int main()
{
printf("%s: ", "func(2,3)");
for (int i = 0; i < 5; i++)
{
foo();
func(2, 3);
}
}
So that macro is a wrapper that prints the function name plus it's parameters as it is invoked with the macro and executes that function specified in the first parameter repeat times (whatever repeat is). If the second parameter is omitted, the function that has that name is simple not invoked before the function mentioned before as in the following example:
int main()
{
MACRO_FN(func(2, 3),, var1, size);
}
Once preprocessed, the code is equivalent to this:
int main()
{
printf("%s: ", "func(2,3)");
for (int i = 0; i < 5; i++)
{
;
func(2, 3);
}
}
Note:
I removed the do while(0) from the equivalent programs for brevity, read this SO article for more information:
answered Nov 19 '18 at 14:11
JabberwockyJabberwocky
26.6k93770
Here is a minimal example:
#define repeat 5 // I added this, because 'repeat' is not mentionned in your question
#define MACRO_FN(test, pre, var1, size)
do {
printf("%s: ", #test);
for (int i = 0; i < repeat; i++) {
pre;
test;
}
} while (0)
void foo()
{
}
void func(int a, int b)
{
}
int main()
{
MACRO_FN(func(2, 3), foo(), var1, size);
}
Once preprocessed, the code is equivalent to this:
int main()
{
printf("%s: ", "func(2,3)");
for (int i = 0; i < 5; i++)
{
foo();
func(2, 3);
}
}
So that macro is a wrapper that prints the function name plus it's parameters as it is invoked with the macro and executes that function specified in the first parameter repeat times (whatever repeat is). If the second parameter is omitted, the function that has that name is simple not invoked before the function mentioned before as in the following example:
int main()
{
MACRO_FN(func(2, 3),, var1, size);
}
Once preprocessed, the code is equivalent to this:
int main()
{
printf("%s: ", "func(2,3)");
for (int i = 0; i < 5; i++)
{
;
func(2, 3);
}
}
Note:
I removed the do while(0) from the equivalent programs for brevity, read this SO article for more information:
answered Nov 19 '18 at 14:11
JabberwockyJabberwocky
26.6k93770
edited Nov 19 '18 at 15:47
answered Nov 19 '18 at 14:11
JabberwockyJabberwocky
26.6k93770
answered Nov 19 '18 at 14:11
JabberwockyJabberwocky
26.6k93770
answered Nov 19 '18 at 14:11
JabberwockyJabberwocky
26.6k93770
26.6k93770
add a comment |
add a comment |
pre and test seem to be two functions.
Based on how it is written, we can guess that pre is a function called before the test.
The double comma has no special meaning. It is just here because the second parameter (pre) was omitted.
Edit: As a side note that kind of macro "should be avoided like plague", as @Lundin put it.
answered Nov 19 '18 at 12:42
XaxetrovXaxetrov
544
add a comment |
pre and test seem to be two functions.
Based on how it is written, we can guess that pre is a function called before the test.
The double comma has no special meaning. It is just here because the second parameter (pre) was omitted.
Edit: As a side note that kind of macro "should be avoided like plague", as @Lundin put it.
answered Nov 19 '18 at 12:42
XaxetrovXaxetrov
544
add a comment |
pre and test seem to be two functions.
Based on how it is written, we can guess that pre is a function called before the test.
The double comma has no special meaning. It is just here because the second parameter (pre) was omitted.
Edit: As a side note that kind of macro "should be avoided like plague", as @Lundin put it.
answered Nov 19 '18 at 12:42
XaxetrovXaxetrov
544
pre and test seem to be two functions.
Based on how it is written, we can guess that pre is a function called before the test.
The double comma has no special meaning. It is just here because the second parameter (pre) was omitted.
Edit: As a side note that kind of macro "should be avoided like plague", as @Lundin put it.
answered Nov 19 '18 at 12:42
XaxetrovXaxetrov
544
edited Nov 19 '18 at 13:22
answered Nov 19 '18 at 12:42
XaxetrovXaxetrov
544
answered Nov 19 '18 at 12:42
XaxetrovXaxetrov
544
answered Nov 19 '18 at 12:42
XaxetrovXaxetrov
544
544
add a comment |
add a comment |
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3
Run the code through the preprocessor and look what the macro expands to.
– Some programmer dude
Nov 19 '18 at 12:36
1
To omit
pre;- maybe? Did you check the pre-processed code?– Sourav Ghosh
Nov 19 '18 at 12:37
I didn't think to check the output of the pre-processor, but I'll do that now
– Jack Evans
Nov 19 '18 at 12:47
2
When invoking a preprocessor macro , "blank" is a valid argument; the call
MACRO_FN(a,,b,c)means thatprewill expand to blank– M.M
Nov 19 '18 at 12:50
2
Please note that macros like these should be avoided like the plague.
– Lundin
Nov 19 '18 at 12:55