You are right that VLA’s are basically always unsafe. The only exception is if you ensure that you never make them larger than a size you would feel safe making a fixed-size array, and in that case you might as well just use a fixed-size array. There is one obscure class of recursive algorithms where … Read more
If coding in C99 or C11, you might want to use flexible array members (you don’t give an explicit dimension, but you should have a convention about it at runtime in your head). typedef struct { unsigned No_Of_Employees; char* Employee_Names[]; // conventionally with No_of_Employees slots }st_employees; As for any array, each slot of a flexible … Read more
Variable length arrays(VLA) are a C99 feature and Visual Studio until recently did not support C99 and I am not sure if it currently supports VLA in the lastest version. gcc on the other hand does support C99 although not fully. gcc supports VLA as an extension outside of C99 mode, even in C++. From … Read more
No they’re not absolutely the same. While both let you store the same number and type of objects, keep in mind that: You can free() a malloced array, but you can’t free() a variable length array (although it goes out of scope and ceases to exist once the enclosing block is left). In technical jargon, … Read more
You’ll have to use memset: memset(board, 0, sizeof board);
For reasons that are not entirely clear to me, almost every time the topic of C99 VLA pops up in a discussion, people start talking predominantly about the possibility of declaring run-time-sized arrays as local objects (i.e. creating them “on the stack”). This is rather surprising and misleading, since this facet of VLA functionality – … Read more
The current C++ standard does not require that compilers support VLAs. However, compiler vendors are permitted to support VLAs as an extension. GCC >= 4.7, for example, does. It was originally proposed that VLAs would appear in C++14, however the proposal did not succeed. They also, ultimately, did not appear in C++17.
Here’s the allocation code (x86 – the x64 code is similar) for the following example line taken from some GCC docs for VLA support: char str[strlen (s1) + strlen (s2) + 1]; where the calculation for strlen (s1) + strlen (s2) + 1 is in eax (GCC MinGW 4.8.1 – no optimizations): mov edx, eax … Read more
Case 1: In char Buffer[MAX_BUF]; Buffer is an array of size MAX_BUF. The allocation technique is called VLA. Case 2: In const int MAX_BUF = 1000; char* Buffer = malloc(MAX_BUF); Buffer is a pointer which is allocated a memory of size MAX_BUF which is 1000. and, an array is not the same as a pointer, … Read more
There are several different pieces at play here. The first is the difference between declaring an array as int array[n]; and int* array = malloc(n * sizeof(int)); In the first version, you are declaring an object with automatic storage duration. This means that the array lives only as long as the function that calls it … Read more