GCC extension __attribute__ ((unused)) for variable attributes
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following is a sample code for GCC variable attribute extension,
#include<stdio.h>
int main(void)
int sam __attribute__((unused))= 10;
int p = sam+1;
printf("n%d" , p);
for the assembly code of above program generated using:
gcc -S sample.c
the .s file dosen't contain the variable sam in it,whereas the output of program is "11" which is correct.
So does the compiler neglect completely the unused variable and not output it in the executable? If so why is the output of program correct?Can anyone explain the working of unused and used variable attributes in gcc.
Thanks
c gcc gcc-extensions
asked Nov 15 '18 at 15:03
Sameeran JoshiSameeran Joshi
84
add a comment |
following is a sample code for GCC variable attribute extension,
#include<stdio.h>
int main(void)
int sam __attribute__((unused))= 10;
int p = sam+1;
printf("n%d" , p);
for the assembly code of above program generated using:
gcc -S sample.c
the .s file dosen't contain the variable sam in it,whereas the output of program is "11" which is correct.
So does the compiler neglect completely the unused variable and not output it in the executable? If so why is the output of program correct?Can anyone explain the working of unused and used variable attributes in gcc.
Thanks
c gcc gcc-extensions
asked Nov 15 '18 at 15:03
Sameeran JoshiSameeran Joshi
84
2
__attribute__((unused))merely influences what warnings the compiler will emit. It makes no difference to code generation and optimisation.
– Toby Speight
Nov 15 '18 at 15:06
Modern compilers are very smart when they optimize. The compiler can see thatsam + 1equals11and can print it directly without using variables.
– Some programmer dude
Nov 15 '18 at 15:10
add a comment |
following is a sample code for GCC variable attribute extension,
#include<stdio.h>
int main(void)
int sam __attribute__((unused))= 10;
int p = sam+1;
printf("n%d" , p);
for the assembly code of above program generated using:
gcc -S sample.c
the .s file dosen't contain the variable sam in it,whereas the output of program is "11" which is correct.
So does the compiler neglect completely the unused variable and not output it in the executable? If so why is the output of program correct?Can anyone explain the working of unused and used variable attributes in gcc.
Thanks
c gcc gcc-extensions
asked Nov 15 '18 at 15:03
Sameeran JoshiSameeran Joshi
84
following is a sample code for GCC variable attribute extension,
#include<stdio.h>
int main(void)
int sam __attribute__((unused))= 10;
int p = sam+1;
printf("n%d" , p);
for the assembly code of above program generated using:
gcc -S sample.c
the .s file dosen't contain the variable sam in it,whereas the output of program is "11" which is correct.
So does the compiler neglect completely the unused variable and not output it in the executable? If so why is the output of program correct?Can anyone explain the working of unused and used variable attributes in gcc.
Thanks
c gcc gcc-extensions
c gcc gcc-extensions
asked Nov 15 '18 at 15:03
Sameeran JoshiSameeran Joshi
84
asked Nov 15 '18 at 15:03
Sameeran JoshiSameeran Joshi
84
asked Nov 15 '18 at 15:03
Sameeran JoshiSameeran Joshi
84
asked Nov 15 '18 at 15:03
Sameeran JoshiSameeran Joshi
84
asked Nov 15 '18 at 15:03
Sameeran JoshiSameeran Joshi
84
84
2
__attribute__((unused))merely influences what warnings the compiler will emit. It makes no difference to code generation and optimisation.
– Toby Speight
Nov 15 '18 at 15:06
Modern compilers are very smart when they optimize. The compiler can see thatsam + 1equals11and can print it directly without using variables.
– Some programmer dude
Nov 15 '18 at 15:10
add a comment |
2
__attribute__((unused))merely influences what warnings the compiler will emit. It makes no difference to code generation and optimisation.
– Toby Speight
Nov 15 '18 at 15:06
Modern compilers are very smart when they optimize. The compiler can see thatsam + 1equals11and can print it directly without using variables.
– Some programmer dude
Nov 15 '18 at 15:10
2
2
__attribute__((unused)) merely influences what warnings the compiler will emit. It makes no difference to code generation and optimisation.– Toby Speight
Nov 15 '18 at 15:06
__attribute__((unused)) merely influences what warnings the compiler will emit. It makes no difference to code generation and optimisation.– Toby Speight
Nov 15 '18 at 15:06
Modern compilers are very smart when they optimize. The compiler can see that
sam + 1 equals 11 and can print it directly without using variables.– Some programmer dude
Nov 15 '18 at 15:10
Modern compilers are very smart when they optimize. The compiler can see that
sam + 1 equals 11 and can print it directly without using variables.– Some programmer dude
Nov 15 '18 at 15:10
add a comment |
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2
__attribute__((unused))merely influences what warnings the compiler will emit. It makes no difference to code generation and optimisation.– Toby Speight
Nov 15 '18 at 15:06
Modern compilers are very smart when they optimize. The compiler can see that
sam + 1equals11and can print it directly without using variables.– Some programmer dude
Nov 15 '18 at 15:10