C++中为何使用int *arr = new int[quantity]而非int arr[quantity]？

Hey there! Great question—this is a super common point of confusion when you're starting out with C++ memory management. Let's break down why the original code uses dynamic allocation with new instead of the variable-length array (VLA) syntax that your compiler happens to support.

Key Reasons for Choosing new Over VLAs: #

• Standard C++ Compliance
  Variable-length arrays like int arr[quantity] are a C99 feature, and they're not part of the official C++ standard (even in C20). Compilers like GCC and Clang support them as an extension, but other major compilers (like MSVC) don't. Using new ensures your code will compile and run correctly on all standard-compliant C compilers, no matter what.

• Avoid Stack Overflow Risks
  VLAs are allocated on the stack, which has a very limited size (usually just a few megabytes). If quantity is large (say, 100,000 or more), your program will crash with a stack overflow. Dynamic allocation with new uses the heap, which has far more available memory—perfect for storing larger datasets.

• Controlled Lifecycle & Flexibility
  Stack-allocated arrays are automatically destroyed when they go out of scope (like when the function ends). With new, you control exactly when the memory is freed (using delete[] arr). This is crucial if you need the array to live beyond the current function, or if you want to pass ownership of the array between functions.

• Established C++ Best Practices
  Even if your compiler supports VLAs, most experienced C++ developers prefer dynamic allocation (or better yet, modern alternatives like std::vector or std::unique_ptr<int[]>) because it's the standard, portable way to handle variable-size arrays. It avoids relying on compiler-specific quirks that could break your code later.

A quick bonus tip: If you're writing modern C++, you might want to skip both new and VLAs entirely and use std::vector<int> arr(quantity)—it's safer (automatically manages memory), more flexible, and 100% standard-compliant!

内容的提问来源于stack exchange，提问作者Autumn