In Visual Studio, can I set conditional breakpoints that can peek variables from another scope?

Question

Look at this code:

void F1() {
    for (int i = 0; i < 100; i ++)
        F2();
}

void F2() {
    for (int i = 0; i < 100; i ++)
        F3();
}

void F3() {
    int a = 0; // break point here
    for (int i = 0; i < 100; i ++)
        a ++;
}

I want to put a break point at the line int a = 0; in F3(), but I only want to pause when i==70 in F1() and i==80 in F2().

That means when I am in F3()'s scope, I have to peek F2()'s and F1()'s local variables. But in actual code, those two variables are not meant to be passed down.

What is the right way to do this?

related, not necessarily a duplicate: https://stackoverflow.com/a/4251470/1132334 (object id approach, object ids are valid in the condition box of a breakpoint) — Cee McSharpface, Apr 26 '21 at 08:21
What I usually do in such cases is to create a global variable for debugging. — Devolus, Apr 26 '21 at 08:22
You cant see out-of-scope variables as they do not exist in another scope. — 0___________, Apr 26 '21 at 08:24
@0___________ inside the program no, but I wouldn't be so sure about MSVC debugger, since it supports the so-called [ObjectID references](https://abhijitjana.net/2010/10/20/how-to-track-an-object-which-is-out-of-scope-while-debugging/). — rustyx, Apr 26 '21 at 08:39

Allen Hu · Answer 1 · 2021-04-26T09:25:50.557

1

Maybe you can add a counter that track the number of times the fonction F3() is called.

//track F3() call of times
private int times = 0;
void F3() {
    int a = 0; // break point if times == 70 || times == 80
    for (int i = 0; i < 100; i ++)
        a ++;    
    //add 1 call of times
    times++;
}

edited Apr 26 '21 at 09:25

answered Apr 26 '21 at 08:52

Allen Hu

141
6

1

code only answer is cool. But perhaps you can add details and explanation. like : "_Maybe you_ want to add a counter that track the number of `times` the fonction `Foo()` is called. That way you may use that to track the number of execution of ... etc" – Self Apr 26 '21 at 09:05
This is indeed a solution. But sometimes what we need is not about counting. For example, maybe the condition I need in `F1()` is `some_array[i] == "Tom"`. – landings Apr 27 '21 at 14:59

score 1 · Accepted Answer · answered Apr 26 '21 at 13:57

If it is possible to change the code, the less interfering code that I can imagine is the following - without using the trick of the hits count of @Maaz.

It is based on using the current thread to "storage" the values.

void F1() {
    for (int i = 0; i < 100; i ++)
    {
        CallContext<Int32>.SetData("i-first", i);
        F2();
    }
}

void F2() {
    for (int i = 0; i < 100; i ++)
    {
        CallContext<Int32>.SetData("i-second", i);
        F3();
    }
}

void F3() {
    int a = 0; // break point here
    for (int i = 0; i < 100; i ++)
        a ++;
}

//Helper class for .Net Core.
//For .Net Framework you can use CallContext.LogicalSetData, CallContext.LogicalGetData
public static class CallContext<T>
{
    static ConcurrentDictionary<string, AsyncLocal<T>> state = 
         new ConcurrentDictionary<string, AsyncLocal<T>>();

    public static void SetData(string name, T data) =>
            state.GetOrAdd(name, _ => new AsyncLocal<T>()).Value = data;

    public static T GetData(string name) =>
            state.TryGetValue(name, out AsyncLocal<T> data) ? data.Value : default(T);
}

The conditional expression for the breakpoint is:

CallContext<Int32>.GetData("i-first") == 70 && CallContext<Int32>.GetData("i-second") == 80

This looks good. Adding some code is OK for me. – landings Apr 27 '21 at 15:03 — landings, Apr 27 '21 at 15:03

score 0 · Answer 3 · answered Apr 26 '21 at 08:31

0

You could set a conditional breakpoint that does a hit test. Set it to hit the value 7081 and it should work.

F2() is called 70 times, and for each of those 70 times, F3() is called 100 times. So, for the 71st loop, i.e. F1()'s i == 70, and 81th sub loop, i.e F2()'s i == 80, a hit test for 70*100 + 81 should work.

answered Apr 26 '21 at 08:31

Standard_101

325
4
14

Doesn't A get reset every time? There is a scope issue. – Self Apr 26 '21 at 09:01
Yes, `a` would. But, to stop at the exact line as the question suggested, this is what I thought of. – Standard_101 Apr 26 '21 at 09:13

score -1 · Answer 4 · answered Apr 26 '21 at 08:21

-1

Yes, Follow below steps

Set the breakpoint on the line you want to debug
Right-click on the breakpoint
Select "Conditions", this will prompt you to the pop-up
Write the condition
Close and Debug.

answered Apr 26 '21 at 08:21

Syed

417
1
6
13

2

how does this address the issue of out-of-scope variables? – Cee McSharpface Apr 26 '21 at 08:22

In Visual Studio, can I set conditional breakpoints that can peek variables from another scope?

4 Answers4