gcc-extensions

I'm trying to work through an issue on a third party library. The issue is the library uses GCC's nested functions buried in a macro, and Clang does not support nested functions and has no plans to do so (cf., Clang Bug 6378 - error: illegal storage class on function ). Here's the macro that's the pain point for me and Clang: #define RAII_VAR(vartype, varname, initval, dtor) \ /* Prototype needed due to http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36774 */ \ auto void _dtor_ ## varname (vartype * v); \ void _dtor_ ## varname (vartype * v) { dtor(*v); } \ vartype varname __attribute__((cleanup(

I have the following code which could not be complied. using namespace std; void f(int); template<typename T1, size_t N> void array_ini_1d(T1 (&x)[N]) { for (int i = 0; i < N; i++) { x[i] = 0; } } What is the proper way to pass the array if the main is something like below. int main() { int a; cin >> a; int n = a / 4; f(n); return 0; } void f(int n) { int arr[n]; array_ini_1d(arr); } error: no matching function to call to array_ini_1d.............. I don't think the compiler can deduce the size of a variable-length array in a template. Also, don't forget to forward declare f before you use it.

I came across this weird C++ program. #include <iostream> using namespace std; int main() { int a = ({int x; cin >> x; x;}); cout << a; } Can anyone explain what is going on? What is this construct called? It assigns user input value to a and prints it out. it is done by using a Statement Expression . Statement Expressions are gnu gcc compiler extension are not supported by the C/C++ standards. Hence any code which uses statement expression is non standard conforming and non portable. The IBM IBM XL C/C++ v7.0 also support Statement Expressions & it's doccumentation explains them aptly:

I had always thought that variable length arrays were not allowed in c++(Refer : Why aren't variable-length arrays part of the C++ standard? ) .But than why does this code compile and work? #include <iostream> using namespace std; int main () { int n; cin >> n; int a[n]; for (int i=0; i<n; i++) { a[i] = i; } for (int i=0; i<n; i++) { cout << a[i] << endl; } } David Heffernan The current C++ standard does not require that compilers VLAs. However, compiler vendors are permitted to support VLAs as an extension. It was originally proposed that VLAs would appear in C++14, however the proposal did