using assert() for debugging

# 17 Dec 2011

hello,

I'd like to use assert statements for debugging my code, but I can't seem to get it to work correctly.

The assert() statement does exist and does work: the execution stops if the condition is false. However, unlike error() there is no debug information printed to stdout, nor are the blue lights of death flashing.

I noticed there was assert functionality in an earlier revision of the mbed library: http://mbed.org/projects/libraries/svn/mbed/trunk/Debug.h?rev=2

Is it still in there ? or do i implement it myself? something like this:

#define my_assert(b) if (!b) error("ASSERT FAILED at %s, line %d.\n", __FILE__, __LINE__);

thanks, Daniel

Dave Van Wagner

# 09 Apr 2012

I have a similar question. How do I use assert() macros with mbed? With the following code I see that the flashing led doesn't happen because the assert stopped, but where does the failure get sent to? How can I flush stderr if processing is stopped? I don't see any output in my USB console except for starting.

#include <mbed.h>
#include <assert.h>

DigitalOut myled(LED1);

int main()
{
    printf("starting\n");

    assert(false);

    printf("finished\n");

    while(1) 
    {
        myled = 1;
        wait(0.2);
        myled = 0;
        wait(0.2);
    }
}

Dave Van Wagner

# 25 Sep 2013

On revisiting this, the following macro works better for me than the one in assert.h

#ifdef NDEBUG
#define assert(expr)
#else
#define assert(expr) \
{ \
    if (!(expr)) \
    { \
        printf("Assertion failed: %s, file %s, line %d\n", #expr, __FILE__, __LINE__); \
        fflush(stdout); \
        exit(-1); \
    } \
}
#endif

Cale McCollough

# 16 Dec 2015

I like to add a debug message and use a Global.h file that defines the USB debugging serial port. This way you can access it from any of your classes. The blinking red and blue lights you notice the assert in case something is obstructing your view of your terminal. It really helps speed up debugging. Its kind of like you got pulled over. If you have an LCD screen and another microcontroller, you can output the assert statement to the screen and bypass a terminal app all together, which is convenient.

#ifndef Included_ProjectName__Global_header
#define Included_ProjectName__Global_header

#include "stdint.h"

#define DebugMode               1

#define Using_mbed          1
#if Using_mbed
#include "mbed.h"
#define nullptr             0
#endif // Using_mbed


#if DebugMode

#define Using_mbed          1
#if Using_mbed
#include "mbed.h"
#define nullptr             0
#endif // Using_mbed

#if DebugMode
#include "mbed.h"

static DigitalOut redLED (LED_RED, 1),
    greenLED (LED_GREEN, 1),
    blueLED (LED_BLUE, 1);

static Serial debug (USBTX, USBRX); // Tx, Rx

static Ticker assertionBlinker;

static void AssertionBlinkerHandler ()
{
    static bool redLEDOn = false;
        
    if (redLEDOn)
    {
        redLED = 0;
        blueLED = 1;
        redLEDOn = false;
    }
    else
    {
        redLED = 1;
        blueLED = 0;
        redLEDOn = true;
    }
}

#define Assert(statement, message) \
{ \
    if (!(statement)) \
    { \
        assertionBlinker.attach (&AssertionBlinkerHandler, 0.2f);  \
        debug.printf("Assert: %s\n\r%s, line %d\n\r", #message, __FILE__, __LINE__); \
        while (true); \
    } \
}

static void ConsoleLine (char token)
{
    debug.putc ('\r');
    for (int i = 0; i < 80; ++i)
        debug.putc (token);
    debug.putc ('\n');
    debug.putc ('\r');
}

#endif // DebugMode

#endif // Included_ProjectName__Global_header

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