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I have a question on external variables in a multifile program.
Quoting from K&R (first addition, page 72)
"By default, external variables are also "global", so that all references to such a variable by the same name (even from functions compiled separately) are references to the same thing."
Here's an example that doesn't work. The variable 'a' in file 1 is external (since it's defined outside of any function) so, according to the above paragraph, it should have the same value in file 2. The
program, however, doesn't compile. If the line "int a" is added to
file 2 it compiles and runs, giving the wrong answer 0. If instead the
line "extern int a" is added then it runs and gives the correct
answer 12. I understand why the last version works, but shouldn't
the first one also (according to K&R)?
Does anyone have any insights to offer?
_____________________file 1____________________________
________________file 2____________________________
Quoting from K&R (first addition, page 72)
"By default, external variables are also "global", so that all references to such a variable by the same name (even from functions compiled separately) are references to the same thing."
Here's an example that doesn't work. The variable 'a' in file 1 is external (since it's defined outside of any function) so, according to the above paragraph, it should have the same value in file 2. The
program, however, doesn't compile. If the line "int a" is added to
file 2 it compiles and runs, giving the wrong answer 0. If instead the
line "extern int a" is added then it runs and gives the correct
answer 12. I understand why the last version works, but shouldn't
the first one also (according to K&R)?
Does anyone have any insights to offer?
_____________________file 1____________________________
#include <iostream>
using namespace std;
int a=6;
int f(int);
main()
{ cout << f(2) << endl;
}int f(int x)
{ return (a*x);
}
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Originally Posted by murschech
Does anyone have any insights to offer?
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Originally Posted by murschech
Here's an example that doesn't work. The variable 'a' in file 1 is external (since it's defined outside of any function) so, according to the above paragraph, it should have the same value in file 2. The program, however, doesn't compile.
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Originally Posted by murschech
If the line "int a" is added to file 2 it compiles and runs, giving the wrong answer 0.
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Originally Posted by murschech
If instead the line "extern int a" is added then it runs and gives the correct answer 12. I understand why the last version works, but shouldn't the first one also (according to K&R)?
[aside]Using K&R1 as a reference for C++98 seems to leave room for a number of gaps.[/aside]
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