GCC provides extensions not found in ISO standard C or C++.
Questions tagged [gcc-extensions]
45 questions
108
votes
1 answer
What is this "[0 ... 255] =" syntax in C?
Refering to js0n.c
The code syntax is as below:
static void *gostruct[] =
{
[0 ... 255] = &&l_bad,
['\t'] = &&l_loop, [' '] = &&l_loop, ['\r'] = &&l_loop, ['\n'] = &&l_loop,
['"'] = &&l_qup,
[':'] = &&l_loop,…
Gaurav K
- 2,864
- 9
- 39
- 68
83
votes
4 answers
What's this C++ syntax that puts a brace-surrounded block where an expression is expected?
I came across this weird C++ program.
#include
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?
Koshimitsu
- 1,144
- 1
- 12
- 19
51
votes
4 answers
What is "..." in switch-case in C code
Here is a piece of code in /usr/src/linux-3.10.10-1-ARCH/include/linux/printk.h:
static inline int printk_get_level(const char *buffer)
{
if (buffer[0] == KERN_SOH_ASCII && buffer[1]) {
switch (buffer[1]) {
case '0' ... '7':
case 'd': …
jasonz
- 1,315
- 1
- 17
- 31
8
votes
2 answers
Are variable length arrays there in c++?
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
using namespace std;
int main () {
…
nikhil_vyas
- 513
- 5
- 16
8
votes
1 answer
How to stop Eclipse CDT from emitting errors due to gcc specific syntax?
I'm writing some code that makes use of computed goto. The syntax checker is flagging every instance of goto *ptr and &&label as syntax error. Is there anyway to stop this?
Addition by alk:
Example for computed gotos (gcc extension):
...
void *…
cleong
- 7,242
- 4
- 31
- 40
7
votes
2 answers
how to explain this expression "int a=({10;});" in C language?
During my C language practice, I face an expression and then I get it simplified as follows:
int a=({10;});
It is a legal expression since it gets past the gcc compiler.
Please focus on this part: ({10;}). Is anybody able to explain it? The more…
kevin
- 765
- 1
- 6
- 16
6
votes
1 answer
Why doesn't GCC's ternary extension support assignment?
GCC has an awesome ternary expression extension to C which allows us to create a statement like this:
int x = some_var ?: 10; // expands to some_var ? some_var : 10
Which is really nice, and while it's not particularly intuitive, it does work. Most…
Richard J. Ross III
- 55,009
- 24
- 135
- 201
5
votes
2 answers
Error: "cannot bind packed field" while inserting data into std::map using insert function
Can somebody tell me the difference between #pragma pack(push,1) and __attribute__((packed))? I am getting a compilation error if I use second type of struct packing which says
cannot bind packed field ‘ABC.abc::a’ to ‘unsigned int&’
But if I…
Harry
- 2,177
- 1
- 19
- 33
5
votes
3 answers
Rewrite GCC cleanup macro with nested function for Clang?
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…
jww
- 97,681
- 90
- 411
- 885
5
votes
3 answers
Are variable-length arrays really not allowed in C90?
I'm reading about VLAs in C Primer Plus, and this book strictly says that the introduction of VLAs to C began with the C99 standard. Whenever I attempt to declare a loop control variable within the header of a for loop, gcc informs me that this…
Theo Chronic
- 1,623
- 2
- 15
- 16
5
votes
2 answers
GCC typeof extension
I don't understand why this works:
/* gcc range extension */
__extension__ static int fn(int n)
{
switch (n) {
case 0: return 0;
case 1 ... 1000: return 1;
default: return -1;
}
}
But this does not:
/* gcc typeof…
David Ranieri
- 39,972
- 7
- 52
- 94
4
votes
1 answer
Why this compound statement as a sequence of statements enclosed by braces and inside parentheses does not appear to be a valid statement expression
Why this compound statement as a sequence of statements enclosed by braces (in GNU C++) and inside parentheses does not appear to be a valid Statement expression.
// my second program in C++
#include
using namespace std;
int main ()
{
…
K.Karamazen
- 176
- 1
- 8
3
votes
4 answers
How to implement Go's defer() in C so that it allows declaring vars?
In this Modern C video there's a trick that allows to postpone execution of a code until the block/scope exits. It's used as follows:
int main()
{
int foo=0, bar;
const char *etc = "Some code before defer";
defer(profile_begin(),…
psprint
- 349
- 1
- 10
3
votes
1 answer
What is the functional difference between "(void) cast" vs. "__attributes__" for silencing unused argument warnings?
Is there any functional difference between marking a virtual method's unused parameter arguments with GCC's __attribute__((unused)) and casting the argument to (void)?
class Other {
virtual int sum(int a, int b, int c);
};
class Example : Other…
ktb
- 1,498
- 10
- 27
3
votes
0 answers
Using gcc/clang C extensions to test if a macro argument is a pointer
Using gcc/tcc/clang's extensions to the C language (C11), is it possible to detect whether
a macro argument has a pointer type?
Details:
I'm using a macro that should take a singly-indirect pointer, but it's tempting to pass a pointer to that…
Petr Skocik
- 58,047
- 6
- 95
- 142