exception: Add exceptions when context creation fails

* Exceptions only fired in constructor when it would initialise with a NULL
  context causing segfaults if used any further
* Adds exception.i requirement to mraa.i for node.js and python support

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

api/mraa/aio.hpp

@@ -24,6 +24,7 @@
 
 #pragma once
 
+#include <stdexcept>
 #include "aio.h"
 
 namespace mraa {
@@ -45,6 +46,9 @@ class Aio {
          */
         Aio(unsigned int pin) {
             m_aio = mraa_aio_init(pin);
+            if (m_aio == NULL) {
+                throw std::invalid_argument("Invalid AIO pin specified - do you have an ADC?");
+            }
         }
         /**
          * Aio destructor

api/mraa/gpio.hpp

@@ -25,6 +25,7 @@
 #pragma once
 
 #include "gpio.h"
+#include <stdexcept>
 
 namespace mraa {
 
@@ -80,12 +81,20 @@ class Gpio {
          * you so this may not always work as expected.
          */
         Gpio(int pin, bool owner=true, bool raw=false) {
-            if (raw)
+            if (raw) {
                 m_gpio = mraa_gpio_init_raw(pin);
-            else
+            }
+            else {
                 m_gpio = mraa_gpio_init(pin);
-            if (!owner)
+            }
+
+            if (m_gpio == NULL) {
+                throw std::invalid_argument("Invalid GPIO pin specified");
+            }
+
+            if (!owner) {
                 mraa_gpio_owner(m_gpio, 0);
+            }
         }
         /**
          * Gpio object destructor, this will only unexport the gpio if we where

api/mraa/i2c.hpp

@@ -25,6 +25,7 @@
 #pragma once
 
 #include "i2c.h"
+#include <stdexcept>
 
 namespace mraa {
 
@@ -48,10 +49,15 @@ class I2c {
          * @param raw Whether to disable pinmapper for your board
          */
         I2c(int bus, bool raw=false) {
-            if (raw)
+            if (raw) {
                 m_i2c = mraa_i2c_init_raw(bus);
-            else
+            }
+            else {
                 m_i2c = mraa_i2c_init(bus);
+            }
+            if (m_i2c == NULL) {
+		throw std::invalid_argument("Invalid i2c bus");
+            }
         }
         /**
          * Closes the I2c Bus used. This does not guarrantee the bus will not

api/mraa/pwm.hpp

@@ -25,6 +25,7 @@
 #pragma once
 
 #include "pwm.h"
+#include <stdexcept>
 
 namespace mraa {
 
@@ -47,12 +48,20 @@ class Pwm {
          * if the pinmapper exported it
          */
         Pwm(int pin, int chipid=-1, bool owner = true) {
-            if (chipid == -1)
+            if (chipid == -1) {
                 m_pwm = mraa_pwm_init(pin);
-            else
+            }
+            else {
                 m_pwm = mraa_pwm_init_raw(pin, chipid);
-            if (!owner)
+            }
+
+            if (m_pwm == NULL) {
+                throw std::invalid_argument("Error initialising PWM on pin");
+            }
+
+            if (!owner) {
                 mraa_pwm_owner(m_pwm, 0);
+            }
         }
         /**
          * Pwm destructor

api/mraa/spi.hpp

@@ -25,6 +25,7 @@
 #pragma once
 
 #include "spi.h"
+#include <stdexcept>
 
 namespace mraa {
 
@@ -44,6 +45,10 @@ class Spi {
          */
         Spi(int bus) {
             m_spi = mraa_spi_init(bus);
+
+            if (m_spi == NULL) {
+                throw std::invalid_argument("Error initialising SPI bus");
+            }
         }
         /**
          * Closes spi bus

api/mraa/uart.hpp

@@ -25,6 +25,7 @@
 #pragma once
 
 #include "uart.h"
+#include <stdexcept>
 
 namespace mraa {
 
@@ -43,6 +44,10 @@ class Uart {
          */
         Uart(int uart) {
             m_uart = mraa_uart_init(uart);
+
+            if (m_uart == NULL) {
+                throw std::invalid_argument("Error initialising UART");
+            }
         }
         /**
          * Uart destructor