How do I initialize a 2D array with 0s when I declare it?
double myArray[3][12] = ?
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7 Answers
double myArray[3][12] = {0};
or, if you want to avoid the gcc warning "missing braces around initializer" (the warning appears with -Wall or, more specifically -Wmissing-braces)
double myArray[3][12] = {{0}};
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If you use the paragraph code blocks (four spaces at the beginning of line) you get syntax hightlighting, which you don't if you use inline blocks (backticks). Commented Nov 6, 2009 at 16:43
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2@Danijel: the
{0}initializer has been valid since C89 (the 1st standardization). Don't know about before that.– pmgCommented Oct 7, 2019 at 13:37
If you want to initialize with zeroes, you do the following:
double myArray[3][12] = { 0 };
If you want to fill in actual values, you can nest the braces:
double myArray[3][3] = { { 0.1, 0.2, 0.3 }, { 1.1, 1.2, 1.3 }, { 2.1, 2.2, 2.3 } };
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+1 for pointing out how to initialize everything ... but why did you shorten the array? :P– pmgCommented Nov 6, 2009 at 16:48
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15I shortened the array because I didn't want to type twelve sets of numbers.– JSBձոգչCommented Nov 6, 2009 at 17:15
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2You might consider using a non-square array for the second example so it's clear which dimension is the inner and which is the outer Commented Jul 13, 2020 at 20:38
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It does not work for me, I have "error: variable-sized object may not be initialized" Commented Nov 8, 2023 at 15:11
The memory layout may be relevant (e.g., for serialization).
myArray[3][2] = { { 0.1, 0.2 }, { 1.1, 1.2 }, { 2.1, 2.2 } };
The first index is the row index is the slowest index. This is known as C order as opposed to F (Fortran) order.
pmg's method is correct, however, note that
double myArray[3][12] = {{}};
will give the same result.
Additionally, keep in mind that
double myArray[3][12] = {{some_number}};
will only work as you expect it when some_number is zero.
For example, if I were to say
double myArray[2][3] = {{3.1}};
the array would not be full of 3.1's, instead it will be
3.1 0.0 0.0
0.0 0.0 0.0
(the first element is the only one set to the specified value, the rest are set to zero)
This question (c initialization of a normal array with one default value) has more information
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1The empty initializer is invalid C (I believe it is valid C++).– pmgCommented Apr 25, 2012 at 8:15
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@pmg or @codyschafer, can anyone point me to the standard where either of your arguments is stated please? initialization using
={ }appears to work in both gcc and g++, but I don't know whether its correct. Commented Oct 7, 2019 at 10:19 -
@GrimFandango: the C11 syntax for initialization does not allow empty initializer (same for C99). If you're using gcc, try
gcc -std=c11 -pedantic ...otherwisegcc ...is the same asgcc -std=gnu11 ...– pmgCommented Oct 7, 2019 at 13:34 -
@GrimFandango: compare C11 6.7.9 (link in my previous comment) with C++14 8.5.1 (sorry, no link)– pmgCommented Oct 8, 2019 at 8:02
You may use
double myArray[3][12] = { 0 };
or
double myArray[3][12];
memset(myArray, 0, sizeof(double) * 3 * 12);
R. Martinho Fernandes
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answered Nov 6, 2009 at 16:46
I think it will be
double myArray[3][12] = {0}
pmg's method works best as it works on the concept that if u initialise any array partially, rest of them get the default value of zero. else, u can declare the array as a global variable and when not initialised, the array elements will automatically be set to the default value (depending on compilers) zero.
