Embedding in C code

Table of Contents

• Introduction
• C Binding Interface

Documentation for linking into a C code base.

Introduction

This section assumes the reader is already familar with developing C codes. The simplist method to link framework code into a C code is to create a C++ function with

extern "C" 

First create a header file c_callable.h

extern "C" {
    void c_callable_function();
}

Next create a source file c_callable.c and add the framework. This example uses the equation of a line example from the making workflows turorial.

//  Include the necessary framework headers.
 
extern "C" {
    void c_callable_function() {
        auto x = graph::variable(3, "x");
 
// Define explicit constant.
        auto m = graph::constant<T> (0.4);
// Define implicit constant.
        const T b = 0.6;
 
// Equation of a line
        auto y = m*x + b;
 
// Auto differentiation.
        auto dydx = y->df(x);
 
        x->set({1.0, 2.0, 3.0});
 
// Create a workflow manager.
        workflow::manager<T> work(0);
        work.add_item({
            graph::variable_cast(x)
        }, {
            y, dydx
        }, {}, NULL, "my_first_kernel", 3);
        work.compile();
 
        work.run();
        work.print(0, {x, y, dydx});
        work.print(1, {x, y, dydx});
        work.print(2, {x, y, dydx});
    }
}

---

C Binding Interface

An alternative is to use the C Language interface. The C binding interface can be enabled as one of the cmake conifgure options. As an example, we will convert the making workflows turorial to use the C language bindings.

#include <graph_c_binding.h>
 
void c_binding() {
    const bool use_safe_math = 0;
    struct graph_c_context *c_context = graph_construct_context(DOUBLE, use_safe_math);
    graph_node x = graph_variable(c_context, 3, "x");
 
    graph_node m = graph_constant(c_context, 0.4);
    graph_node b = graph_constant(c_context, 0.6);
 
    graph_node y = graph_add(c_context, graph_mul(c_context, m, x), b);
    graph_node dydx = graph_df(c_context, y, x);
 
    double temp[3];
    temp[0] = 1.0;
    temp[1] = 2.0;
    temp[2] = 3.0;
    graoh_set_variable(c_context, x, temp);
 
    graph_set_device_number(c_context, 0);
    graph_node inputs[1];
    inputs[0] = x;
    graph_node outputs[2];
    outputs[0] = y;
    outputs[1] = dydx;
    graph_add_item(c_context, inputs, 1, outputs, 2, NULL, NULL, 0, NULL,
                   "x", 3);
    graph_compile(c_context);
    graph_run(c_context);
    graph_node inputs2[3];
    inputs2[0] = x;
    inputs2[1] = y;
    inputs2[2] = dydx;
    graph_print(c_context, 0, inputs2, 3);
    graph_print(c_context, 1, inputs2, 3);
    graph_print(c_context, 2, inputs2, 3);
 
    graph_destroy_context(c_context);
}