Thursday 30 June 2016

c - How to initialize all members of an array to the same value?




I have a large array in C (not C++ if that makes a difference). I want to initialize all members to the same value. I could swear I once knew a simple way to do this. I could use memset() in my case, but isn't there a way to do this that is built right into the C syntax?


Answer



Unless that value is 0 (in which case you can omit some part of the initializer
and the corresponding elements will be initialized to 0), there's no easy way.



Don't overlook the obvious solution, though:



int myArray[10] = { 5, 5, 5, 5, 5, 5, 5, 5, 5, 5 };



Elements with missing values will be initialized to 0:



int myArray[10] = { 1, 2 }; // initialize to 1,2,0,0,0...


So this will initialize all elements to 0:



int myArray[10] = { 0 }; // all elements 0



In C++, an empty initialization list will also initialize every element to 0.
This is not allowed with C:



int myArray[10] = {}; // all elements 0 in C++


Remember that objects with static storage duration will initialize to 0 if no
initializer is specified:



static int myArray[10]; // all elements 0



And that "0" doesn't necessarily mean "all-bits-zero", so using the above is
better and more portable than memset(). (Floating point values will be
initialized to +0, pointers to null value, etc.)


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