cannot convert 'double (*)[10]' to 'double*' for argument - c++

Question

Please help solving the compile time error. I have the declaration in different files as shown below
type.h
extern block posTime(const int row[MAX_ROW], int Flag, int n,double Time[]=0 );
a.cc
block posTime( const int row[MAX_ROW],
int Flag,
int n,
double* eraseTime[]
)
...
eraseTime[0]=test[1];
..
b.cc
...
double eraseTime[MAX_ROW];
block newB = posTime (0,0,0,&eraseTime);
the last line block newB = posTime (0,0,0,&eraseTime); gives me the error, cannot convertdouble (*)[10] to double* for argument 4
I want to upadte the eraseTime in a.cc and use back in b.cc. Can I do that?

Answer 1

Working solution (GCC 4.9.0 with C++11)
test.hpp
#define MAX_ROW 10
extern double posTime(const int row[MAX_ROW], int Flag, int n,double Time[]=0 );
test1.cpp
#include "test.hpp"
double posTime( const int row[MAX_ROW],
int Flag,
int n,
double* eraseTime
)
{ eraseTime[0] = 2; eraseTime[1] = 3; return eraseTime[0]; }
test.cpp
#include <iostream>
#include "test.hpp"
double eraseTime[MAX_ROW] { 1, 2, 3, 4, 5, 6 ,7, 8, 9, 10 };
int main() {
double newB = posTime (0,0,0,eraseTime);
std::cout << "result: " << newB << std::endl;
for (auto v : eraseTime) {
std::cout << v << std::endl;
}
return 0;
}
compilation command:
g++ -std=c++11 -o e:\test.exe e:\test.cpp e:\test1.cpp
or double eraseTime[MAX_ROW], if you are using MAX_ROW in int row i don't see why not in eraseTime (probably some call location not in the sample restrict this use) or double* eraseTime.
Recommended change to use std::array (constant size) or std::vector (dynamic size).

Answer 2

There are multiple issues here:
The signature in the header and in the implementation file are not the same: The header declares the last argument of posTime() to be of type double* (yes, pointer, not array!), while the implementation declares it to be of type double** (again, the array specification is converted to a pointer declaration because it is a function argument declaration).
The result is, that the implementation declares an overload to the function declared in the header, not an implementation for it.
When you take the address of an array, you get a pointer to an array, i. e. a value of type double (*)[MAX_ROW]. This is incompatible to a double**, which is what your compiler is complaining about. To create a variable of this type, you must use the syntax double (*myArrayPointer)[MAX_ROW];. The parentheses are important because the array subscript operator has a higher precedence than the dereference operator, with the consequence that double* myPointerArray[MAX_ROW]; declares an array of MAX_ROW pointers to doubles.
If you want to pass the array as a pointer to an array, you need to declare your function as
extern block posTime(const int row[MAX_ROW], int Flag, int n,double (*Time)[MAX_ROW]=0 );
This has the advantage that you get type checking on the length of the array, but the disadvantage that you cannot accept arrays of dynamic size. If you need this flexibility, the normal approach is to pass a pointer to the first element:
extern block posTime(const int row[MAX_ROW], int Flag, int n,double *Time=0 );
called with
block newB = posTime (0,0,0,eraseTime);
The call relies on array-pointer-decay to make a double* from your array identifier.