strange difference between gcc versions

[Christof Warlich]

Hi,

the following compiles with gcc 2.95.3 but gives this error
with gcc 3.4.4:

~/tmp> gcc tst.cc
tst.c: In function `int main()':
tst.c:4: error: data member may not have variably modified type
`int[((unsignedint)((int)i))]'

int main(void) {
int i = 2;
struct X {
int a;
} x;
return 0;
}

while

int main(void) {
int i = 2;
int a;
return 0;
}

comiles with both gcc versions.

Any ideas why the newer gcc version only allows to create a dynamic
array, but not a dynamic type on the stack? Even more confusing,
both examples compile fine even with gcc 3.4.4 as C-module, i.e.

gcc tst.c

Christof

 

[Phlip]

int main(void) {
int i = 2;
struct X {
int a;

Both nested types accessing automatic (local) variables, and arrays
dimensioned via integers that are not compile time constants, are on-topic
on a newsgroup or mailing list discussing gcc.

This newsgroup is only qualified to discuss Stardard C++, which decrees that
all arrays, without 'new', must size via compile-time constants, and that
nested classes can only access static things in the nesting class or
function.

Your trouble with g++ might be due to compiler specific extensions which ran
into the technical reasons for these restrictions.