http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54583
Bug #: 54583
Summary: Spurious warning: value computed is not used with
variable-size array
Classification: Unclassified
Product: gcc
Version: 4.6.3
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: stuff0...@pobox.com
When declaring a two-dimensional array with variable-length second dimension,
there is a warning "value computed is not used". For example:
$ cat warn1.cpp
void fred(){
int n=10;
double (*x)[n];
}
$ g++ -c warn1.cpp -Wall
warn1.cpp: In function ‘void fred()’:
warn1.cpp:3:16: warning: value computed is not used [-Wunused-value]
warn1.cpp:3:12: warning: unused variable ‘x’ [-Wunused-variable]
The second warning ("unused variable") is to be expected of course, and is not
the subject of this bug report. I don't believe the fact that x isn't used is
relevant to the first warning, so code that uses x is omitted in the above
example in the interests of constructing a minimal example. But to check, here
is a longer example that uses x:
$ cat warn2.cpp
#include <stdio.h>
#include <stdlib.h>
#define M 10
void fred(){
int a,b,n;
n=10;
double (*x)[n];
x=(double(*)[n])malloc(M*n*sizeof(double));
for(a=0;a<M;a++)for(b=0;b<n;b++)x[a][b]=3;
for(a=0;a<M;a++)for(b=0;b<n;b++)printf("%g\n",x[a][b]);
}
$ g++ -c warn2.cpp -Wall
warn2.cpp: In function ‘void fred()’:
warn2.cpp:8:16: warning: value computed is not used [-Wunused-value]
g++ --version
g++ (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3
...
