Accessing the content of a variable array with ctypes

I use ctypes to access a file reading C function in python. As the read data is huge and unknown in size I use **float in C .

int read_file(const char *file,int *n_,int *m_,float **data_) {...}

The functions mallocs an 2d array, called data, of the appropriate size, here n and m, and copies the values to the referenced ones. See following snippet:

*data_ = data;
*n_ = n;
*m_ = m;

I access this function with the following python code:

p_data=POINTER(c_float)
n=c_int(0)
m=c_int(0)
filename='datasets/usps'
read_file(filename,byref(n),byref(m),byref(p_data))

Afterwards I try to acces p_data using contents, but I get only a single float value.

p_data.contents
c_float(-1.0)

My question is: How can I access data in python?

What do you recommended? Please don't hesitate to point out if I left something unclear!