Скачать или смотреть Understanding the SIGTRAP Error in C+ + and OpenGL: Debugging Small Float Arrays

Discover how a misunderstanding in memory allocation can lead to SIGTRAP errors in C+ + OpenGL programs, especially when handling small float arrays.
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Understanding the SIGTRAP Error in C+ + and OpenGL

When working on graphics programming with C+ + , few things are as frustrating as encountering a cryptic error message like SIGTRAP. This signal indicates that your program has hit a trap, usually during debugging, suggesting a serious issue in your code. This post delves into a common scenario that can lead to this error, particularly when using small float arrays with OpenGL.

The Problem

In the code snippet that prompted this discussion, a float array is being allocated dynamically using new[] and subsequently filled with vertex and normal data for a 3D object represented by faces. The key points to note are:

A dynamic array of GLfloat (float) is created based on the number of faces in an object.

Data is filled into this array in a nested loop, which is designed to take into account the vertices and normals of each face.

The array is eventually used with OpenGL’s glBufferData call to send the data to the GPU.

The program crashes intermittently with a SIGTRAP error or an exit code signaling memory corruption.

The Solution

Memory Allocation and Data Writing Misconception

Upon a closer examination, the issue lies in a fundamental misunderstanding regarding how many floats are being written into the allocated memory space. Let’s break it down:

Array Allocation: The code allocates space for vertexBufferSize, which is calculated as:

[[See Video to Reveal this Text or Code Snippet]]

Data Population: During the population of the vertexBuffer, the nested loop actually writes 32 floats for each face due to:

Four vertices per face

Eight floats written per vertex (4 coordinates + 4 normals)

Here's the problematic piece of code:

[[See Video to Reveal this Text or Code Snippet]]

This leads to a total data write of:

8 floats (per vertex) * 4 vertices = 32 floats

However, because only 24 were allocated, the code writes out of bounds.

The Consequences

Writing outside the bounds of an allocated memory area can cause undefined behavior, which may lead to the following issues:

Intermittent crashes (as observed here).

Memory corruption checks failing, resulting in error codes like 0xC0000374.

Correcting the Mistake

To resolve this error, you need to adjust your memory allocation to accommodate the extra floats:

Change the allocation line to correctly reflect that you're writing 32 floats per face:

[[See Video to Reveal this Text or Code Snippet]]

With this adjustment, your program should function correctly when dealing with arrays of both small and large sizes without throwing SIGTRAP errors.

Conclusion

Debugging memory-related issues in C+ + can sometimes be a challenge, especially with dynamic memory allocation and external libraries like OpenGL. Always verify that the amount of memory you allocate matches your data requirements. In this case, recognizing the number of floats being written per face was crucial in avoiding buffer overflows and ensuring stable execution.

By applying proper memory management and being conscious of how data is populated, you can eliminate SIGTRAP errors and improve the robustness of your applications. Happy coding!