October 25, Pavia, Italy
November 6-8, Berlin, Germany
November 3-8, Kona, HI, USA
By Meeting C++ | Oct 3, 2014 07:49 AM | Tags: performance intermediate efficiency c++14 c++11 boost basics
I've written down some basic thinking on new and new standards:
Insights into new and C++
by Jens Weller
From the article:
Every now and then, I've been thinking about this. So this blogpost is also a summary of my thoughts on this topic, dynamic memory allocation and C++. Since I wrote the blog entries on smart pointers, and C++14 giving us make_unique, raw new and delete seem to disappear from C++ in our future code...
By Blog Staff | Oct 3, 2014 05:34 AM | Tags: None
Quick A: std::call_once.
Recently on StackOverflow:
Standard library function for running a function only once
Is there some standard library function/class the behaviour of this lambda expression:
void some_func(int some_arg, float some_other_arg){ static int do_once = ([](){ // will be run once upon first function call but never again return 0; // dummy return value })(); // will always run }t feels like such a hack to write this, but I can't think of another way of doing this other than simply calling the function in
main, but what I'm actually doing depends upon template parameters and I need to keep it as generic as possible.For context: I register a function with
atexitfor every different template parameter, but only once: the first time it is called.
By Blog Staff | Oct 2, 2014 09:40 AM | Tags: None
On Sticky Bits:
Templates of Templates
by Feabhas
From the article:
In this brief article we’ll have a look at the topic of building template classes whose parameters are themselves templates.
I’m assuming you’re reasonably familiar with template classes. If not, here’s a quick introduction...
By Blog Staff | Oct 1, 2014 09:47 AM | Tags: basics
Quick A: Yes, smart pointers replace owning raw pointers, and you should prefer smart pointers in new code. Raw pointers and references are still appropriate to pass parameters down a stack.
Recently on SO:
C++ 11 Smart Pointer usage
I have a question about smart pointers in c++ 11. I've started to have a look at C++ 11 (I usualy program in c#) and read some thing about smart pointers. Now i have the question, does smart pointers completely replace the "old" style of pointers, should i always use them?
By Blog Staff | Oct 1, 2014 06:16 AM | Tags: None
We don't normally link to pleas to spam mass-email anyone, never mind Bjarne Stroustrup, but we just had to share this heartfelt plea because it would be Good for the World. (Sorry, Dr. Stroustrup!)
But even if you don't email him, read or re-read D&E. It's still quite current.
And In the Beginning...
by Tony DaSilva
From the article:
I’m on my second pass through Bjarne Stroustrup’s "The Design And Evolution Of C++". In the book...
By Blog Staff | Sep 30, 2014 09:51 AM | Tags: None
Quick A: Because noexcept doesn't have to keep track of stack unwinding.
noexcept, stack unwinding, and performance
The following draft from Scott Meyers new C++11 book says (page 2, lines 7-21)
The difference between unwinding the call stack and possibly unwinding it has a surprisingly large impact on code generation. In a
noexceptfunction, optimizers need not keep the runtime stack in an unwindable state if an exception would propagate out of the function, nor must they ensure that objects in anoexceptfunction are destroyed in the inverse order of construction should an exception leave the function. The result is more opportunities for optimization, not only within the body of anoexceptfunction, but also at sites where the function is called. Such flexibility is present only fornoexceptfunctions. Functions with “throw()” exception specifications lack it, as do functions with no exception specification at all.In contrast, section 5.4 of "Technical Report on C++ Performance" describes the "code" and "table" ways of implementing exception handling. In particular, the "table" method is shown to have no time overhead when no exceptions are thrown and only has a space overhead.
My question is this - what optimizations is Scott Meyers talking about when he talks of unwinding vs possibly unwinding? Why don't these optimizations apply for
throw()? Do his comments apply only to the "code" method mentioned in the 2006 TR?
By Blog Staff | Sep 29, 2014 12:24 AM | Tags: intermediate
Recently on StickyBits, a nice primer on variadics:
Variadic Templates
by feabhas
From the article:
In this article we’re going to look at a new feature of templates in C++11 -- the concept of the variadic template.
Variadic templates allow us to create functions and classes, not only with generic types, but also a variable number of generic types.
If you haven’t been following along with the template articles, I’d suggest you read this article first before continuing.
By Blog Staff | Sep 29, 2014 12:09 AM | Tags: None
Bulldozer00's appreciation for Alex Stepanov's introduction for Bjarne Stroustrup at CppCon. We already linked to the video last week -- but if you didn't watch it then, do yourself a favor and spend 6 minutes now getting your workweek off to a great start.
A Grand Introduction
by Tony DaSilva
From the article:
"We should not be ashamed of bits. We should be proud of them." -- Alex Stepanov
You may not interpret it in the same way as I did, but I found this cppcon conference introduction of Bjarne Stroustrup by programming scholar Alex Stepanov very moving...
By Blog Staff | Sep 24, 2014 02:49 AM | Tags: intermediate constexpr
Quick A: Yes, when the string being traversed is itself a constant expression, such as a string literal.
Recently on StackOverflow:
Computing length of a C string at compile time. Is this really a constexpr?
I'm trying to compute the length of a string literal at compile time. To do so I'm using following code:
#include <cstdio> int constexpr length(const char* str) { return *str ? 1 + length(str + 1) : 0; } int main() { printf("%d %d", length("abcd"), length("abcdefgh")); }Everything works as expected, the program prints 4 and 8. The assembly code generated by clang shows that the results are computed at compile time:
0x100000f5e: leaq 0x35(%rip), %rdi ; "%d %d" 0x100000f65: movl $0x4, %esi 0x100000f6a: movl $0x8, %edx 0x100000f6f: xorl %eax, %eax 0x100000f71: callq 0x100000f7a ; symbol stub for: printfMy question: is it guaranteed by the standard that length function will be evaluated compile time?
If this is true the door for compile time string literals computations just opened for me... for example I can compute hashes at compile time and many more...
By Blog Staff | Sep 23, 2014 10:41 AM | Tags: basics
Quick A: Because return local_obj; automatically treats it as an rvalue. After all, you won't be using it any more.
When this FAQ came up again recently on SO, the answer was to refer to this previous Q&A:
Returning
unique_ptrfrom functions
unique_ptr<T>does not allow copy construction, instead it supports move semantics. Yet, I can return aunique_ptr<T>from a function and assign the returned value to a variable...unique_ptr<int> foo() { unique_ptr<int> p( new int(10) ); return p; // 1 //return move( p ); // 2 }The code above compiles and works as intended. So how is it that line
1doesn't invoke the copy constructor and result in compiler errors? If I had to use line2instead it'd make sense (using line2works as well, but we're not required to do so)....