Скачать или смотреть Resolving the "subscripted value is neither array nor pointer nor vector" Error in C Programming

Discover how to fix the "subscripted value is neither array nor pointer nor vector" error in C by understanding how to correctly handle 2D arrays and pointers with practical examples.
---
This video is based on the question https://stackoverflow.com/q/65083354/ asked by the user 'Peter M' ( https://stackoverflow.com/u/7555058/ ) and on the answer https://stackoverflow.com/a/65083385/ provided by the user 'Schwern' ( https://stackoverflow.com/u/14660/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Subscripted value is neither array nor pointer nor vector in C program

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding and Fixing the "Subscripted Value is Neither Array nor Pointer nor Vector" Error in C Programming

If you've encountered the error message "subscripted value is neither array nor pointer nor vector" while working with C programming, you're not alone. This frustrating issue often stems from incorrectly handling arrays and pointers. In this post, we'll unravel this error, particularly in the context of reconstructing an image from its segmented parts, and provide a step-by-step guide to fix the issue effectively.

The Problem

In a C program designed to reconstruct an image composed of four quadrants, the following structure is used:

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

This structure is crucial as each subBlock contains a quarter of the total image, represented as a pointer to an array (or more accurately, a 2D array).

When attempting to assemble these blocks back into a single image, the following line throws an error:

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

The error appears for each instance where this line is referenced, indicating a misunderstanding between pointers and arrays.

Analyzing the Source of the Error

Understanding the Structure:

The vertMask in subBlock is an unsigned char* (pointer), not a complete two-dimensional array. Therefore, accessing it with two indices like an array (i.e., vertMask[i][j]) leads to the error.

subBlockList[x].vertMask[i] merely retrieves a single unsigned char, not a 1D or 2D array. Essentially, vertMask[i][j] doesn’t exist in this context.

The Flow of Data:

The program attempts to pull data from a pointer as if it were an array with a certain number of dimensions, causing a mismatch reference.

The Solution

To resolve this issue, we need to change the way we manage our 2D data stored in pointers. Here are the steps to fix the error:

Step 1: Allocate Memory for the 2D Array

When you're using pointers to represent 2D arrays, ensure that memory is allocated dynamically. Modify your implementation of verticalMask like so:

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

This adjustment ensures that you have actual 2D arrays for your mask.

Step 2: Access the Data Correctly

Revise how you fill out subImageTempHolder to correctly access vertMask, like so:

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

Step 3: Don’t Forget to Free Memory

Whenever you allocate memory using malloc, make sure to free it afterward to avoid memory leaks:

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

Conclusion

Handling pointers and arrays in C can be tricky. The "subscripted value is neither array nor pointer nor vector" error serves as a reminder to take care in managing memory. By understanding the differences between pointers and arrays, along with proper memory allocation for 2D array representation, you can effectively troubleshoot and fix similar errors in your programming endeavors.

Remember: Always ensure your data structure conforms to how you intend to access it.

For further reading, explore the nuances of memory management in C and ensure you're familiar with pointer arithmetic and dynamic memory allocation.