What does " = 0" here mean?

int foo (int a , int b = 0)

I just read this code. I don't understand what " = 0" means?

I would also like to know why int foo (int a = 0, int b) d开发者_开发百科oes not compile.

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b is a parameter with a default value of 0. So the function can be called (e.g.):

foo(3, 4)

with a and b equal to 3 and 4

or:

foo(5)

with a and b equal to 5 and 0.

int foo (int a=0, int b)

is wrong because default parameters can only appear at the end. Imagine you had:

int foo (int a = 0, int b, int c = 1)

and called it like:

foo(3, 4)

The compiler wouldn't know which you were omitting. To avoid such situations, you can't put a default parameter before a non-default one.

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See

Default Argument

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It sets the default value for the parameter "b" to the function foo, so that the call foo(345) is equivalent to the call foo(345, 0)