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$expose

Version information

Introduced in version v0.1

This macro is considered stable

About

The $expose macro allows v5dbg to expose variables to the debugger. The exposed variables can be viewed and modified later using debugger commands such as print

Why do I need to use this macro?

V5dbg cannot see where local variables are in memory, see the engineering page for more information.

Notes

Required environment

  • This macro requires the debug server to have been initialized before being called.
  • This macro requires the current thread to be supervised with $ntask or V5Dbg_Init
  • This macro requires the current function to be debuggable
Potential memory error

The $expose macro allows you to expose memory which should be marked as const. For example the following code is valid:

#include "v5dbg/debug.h"

void funcWithParams(const std::string &data)
{
    $function

    $expose(data);
}

void opcontrol()
{
    $ntask
    $function

    funcWithParams("Hello this usually cannot be changed!");
}

Using the debugger you can set the value of the data parameter even though in standard C++ this would result in a compiler error.

Setting the value will usually be fine but it should be classified as undefined behavior.

Examples

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#include "v5dbg/debug.h"

void
opcontrol()
{
    $ntask
    $function

    int i = 0; // Incrementor

    float randomData = 0;
    $expose(randomData); // (1)

    while (true)
    {
        // Add some junk to our variable
        randomData += (i * 5) / 3.3333;

        pros::delay(300);

        i++;
    }
}
  1. Here we allocate a new float variable on the stack and expose it with $expose. We only need to do this when a variable is allocated and any changes made to the variable afterwards will be automatically reflected in the debugger.
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#include "v5dbg/debug.h"

void
printAndSleep(const std::string &p)
{
    $function

    $expose(p); // (1)

    pros::lcd::print(1, "%s", p.c_str()); // Print our data to the screen

    pros::delay(300); // Wait 300ms
}

void
opcontrol()
{
    $ntask
    $function

    int i = 0;
    $expose(i); // (2)
    while (true)
    {
        printAndSleep("Hello World");

        i++;
    }
}
  1. We can expose arguments, even references! This value with show up in a different stack frame from opcontrol
  2. Expose our variable i here, this will show up in a different stack frame from the $expose in printAndSleep