Statically Checked

14 October 2016
Contents[Show]

static_assert is the tool in modern C++ to make your code safe.

static_assert

The usage of static_assert is relatively easy. static_assert requires an expression and a string. The expression must be a predicate that can be evaluated at compile time. Predicate means the expression returns true or false. If the expression evaluates to false you will get at compile time an error message with the string as a message. Of course, you get no executable.

 

Rainer D 6 P2 540x540Modernes C++ Mentoring

Be part of my mentoring programs:

 

 

 

 

Do you want to stay informed about my mentoring programs: Subscribe via E-Mail.

There are a few points you have to keep in your mind.

  • The static_assert expression will be evaluated at compile-time, and you have no runtime overhead.
  • Expressions that can be evaluated at compile time are called constant expressions. I have much to tell about the new keyword constexpr; but in a later post.
  • You can use static_assert expressions in all parts of your program. Therefore, Putting general requirements on your source code in a separate header is a good idea. The result is, the static_assert expression will be automatically verified at compile time if you include the header. 

Here is the code example to static_assert.

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
 
// static_assert.cpp

#include <string>

static_assert(sizeof(void*) == 4 ,"32-bit adressing is required!");
static_assert(sizeof(void*) >= 8 ,"64-bit adressing is required!");

template < typename T, int Line, int Column >
struct Matrix{
   static_assert(Line >= 0, "Line number must be positive.");
   static_assert(Column >= 0, "Column number must be positive.");
   static_assert( Line + Column > 0, "Line and Column must be greater than 0.");
};

int main() {
  
  static_assert(sizeof(int) == sizeof(long int),"int and long int must be of the same length.");
  
  Matrix<int,10,5> intArray;
  Matrix<std::string,3,4> strArray;
  Matrix<double,0,1> doubleArray;
  Matrix<long long,1,0> longArray;
  
  Matrix<char,0,0> charArray;

}

 

The program uses static_assert in the global scope (lines 5 and 6); it uses it in the class scope (lines 10 - line 12); uses it in the local scope (line 17). One of the two assertions in lines 5 and 6 must inevitably fall. The assertions in the class definition guarantee, on the one hand, that the number of columns and lines must be greater than 0, and it guarantees, on the other hand, that the sum has to be positive. That's why the template instantiation in line 14 is invalid. On my computer int is more minor than long int. The C++ standard guarantees the reverse relation.

Let's have a look at the broken run of my compiler.

static assert

What's next?

The power of static_assert is due to what can be evaluated at compile time. Glad we have the new type-traits library in C++11. The powerful type-traits library empowers you to check, compare and change types at compile time. But this is the story of the next post.

 

 

 

 

Thanks a lot to my Patreon Supporters: Matt Braun, Roman Postanciuc, Tobias Zindl, G Prvulovic, Reinhold Dröge, Abernitzke, Frank Grimm, Sakib, Broeserl, António Pina, Sergey Agafyin, Андрей Бурмистров, Jake, GS, Lawton Shoemake, Animus24, Jozo Leko, John Breland, Venkat Nandam, Jose Francisco, Douglas Tinkham, Kuchlong Kuchlong, Robert Blanch, Truels Wissneth, Kris Kafka, Mario Luoni, Friedrich Huber, lennonli, Pramod Tikare Muralidhara, Peter Ware, Daniel Hufschläger, Alessandro Pezzato, Bob Perry, Satish Vangipuram, Andi Ireland, Richard Ohnemus, Michael Dunsky, Leo Goodstadt, John Wiederhirn, Yacob Cohen-Arazi, Florian Tischler, Robin Furness, Michael Young, Holger Detering, Bernd Mühlhaus, Matthieu Bolt, Stephen Kelley, Kyle Dean, Tusar Palauri, Dmitry Farberov, Juan Dent, George Liao, Daniel Ceperley, Jon T Hess, Stephen Totten, Wolfgang Fütterer, Matthias Grün, Phillip Diekmann, Ben Atakora, Ann Shatoff, and Rob North.

 

Thanks, in particular, to Jon Hess, Lakshman, Christian Wittenhorst, Sherhy Pyton, Dendi Suhubdy, Sudhakar Belagurusamy, Richard Sargeant, Rusty Fleming, John Nebel, Mipko, Alicja Kaminska, and Slavko Radman.

 

 

My special thanks to Embarcadero CBUIDER STUDIO FINAL ICONS 1024 Small

 

My special thanks to PVS-Studio PVC Logo

 

My special thanks to Tipi.build tipi.build logo

 

My special thanks to Take Up Code TakeUpCode 450 60

 

Seminars

I'm happy to give online seminars or face-to-face seminars worldwide. Please call me if you have any questions.

Bookable (Online)

German

Standard Seminars (English/German)

Here is a compilation of my standard seminars. These seminars are only meant to give you a first orientation.

  • C++ - The Core Language
  • C++ - The Standard Library
  • C++ - Compact
  • C++11 and C++14
  • Concurrency with Modern C++
  • Design Pattern and Architectural Pattern with C++
  • Embedded Programming with Modern C++
  • Generic Programming (Templates) with C++

New

  • Clean Code with Modern C++
  • C++20

Contact Me

Modernes C++,

RainerGrimmDunkelBlauSmall

 

Tags: static_assert

Comments   

0 #1 visit this hyperlink 2016-11-29 06:11
This article will help the internet visitors for creating new web site
or even a weblog from start to end.
Quote

Stay Informed about my Mentoring

 

Mentoring

English Books

Course: Modern C++ Concurrency in Practice

Course: C++ Standard Library including C++14 & C++17

Course: Embedded Programming with Modern C++

Course: Generic Programming (Templates)

Course: C++ Fundamentals for Professionals

Course: The All-in-One Guide to C++20

Course: Master Software Design Patterns and Architecture in C++

More Profiles

Contact

Subscribe to the newsletter (+ pdf bundle)

Categories

All tags

Blog archive

Source Code

Most Popular Posts

Visitors

Today 3620

Yesterday 5555

Week 33828

Month 55502

All 12133711

Currently are 160 guests and no members online

Kubik-Rubik Joomla! Extensions

Latest comments