Set default parameter of a function as an array [duplicate]
Possible Duplicate:
Default values for array arguments
How do I give an array as the default parameter to a function? I tried this:
void drawCircle(float radius, GLfloat colour[3]={2.0, 3.0, 4.0}, bool do=true) {
...
}
The part GLfloat colour[3]={2.0, 3.0, 4.0}
gives me an error. Is this possible in C++?
In C++, You cannot pass a complete block of memory by value as a parameter to a function, but You are allowed to pass its address.
So NO, you cannot do that atleast in C++03.
You can do this:
GLfloat defaultColor[3] = {2.0, 3.0, 4.0};
void drawCircle(float radius, GLfloat colour[3]= defaultColor, bool do=true)
{
}
You cannot pass an array by value, and so you cannot do that.
So the workaround is, overload the function as:
void drawCircle(float radius, GLfloat *colour, bool pleaseDo)
{
//...
}
void drawCircle(float radius, GLfloat *colour)
{
drawCircle(radius, colour, true);
}
void drawCircle(float radius)
{
GLfloat colour[3]={2.0, 3.0, 4.0};
drawCircle(radius, colour, true);
}
drawCircle(a,b,c); //calls first function
drawCircle(a,b); //calls second function
drawCircle(a); //calls third function
Second and third function eventually call the first function!
Also note that do
is a keyword, so you cannot use it as variable name. I replaced it with pleaseDo
:D
You can define your default value as a global variable. Then, use this global variable as default argument to the function.
GLfloat default_colour[3] = {2.0, 3.0, 4.0};
void drawCircle(float radius, GLfloat colour[3] = default_colour, bool doit = true)
{
}
Btw, do
is a keyword, you cannot use it as a parameter name.
You can't quite do what you want to do but this solution works on my compiler:
static GLFloat DefaultColour[]={2.0,3.0,4.0}
void drawCircle(float radius, GLfloat colour[]=DefaultColour, bool do=true) {
...
}
I think that the Initializer Lists feature from C++11 can help in your question.
void drawCircle(float radius, std::initializer_list<float> colors = {0.9f, 0.2f, 0.7f}, bool do=true)
{
if (colors.size() == 3)
{
// parse the values...
}
...
}
// and then...
drawCircle(10.0f);
Unfortunately I'm not sure that this feature is up on your compiler :(
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