[*] What is its purpose, why was it added? Purpose is seen when a variable length two dimentional array is used as a function parameter. The function int foo(int n, int m, int a[n][m]) {…} can be prototyped as any of the following int foo(int , int, int [][*]); int foo(int , int, int a[*][*]); … 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
In order to answer the question, we should first clear up some concepts. What is an array and how can it be used? And what is the code in the question, if not an array? What is an array? The formal definition of an array is found in the C standard, ISO 9899:2011 6.2.5/20 Types. … Read more
Obviously a hack… but a way of squaring a number without using the * operator (this was a coding contest requirement). (&a)[n] is equivalent to a pointer to int at location (a + sizeof(a[n])*n) and thus the entire expression is (&a)[n] -a = (a + sizeof(a[n])*n -a) /sizeof(int) = sizeof(a[n])*n / sizeof(int) = sizeof(int) * … Read more
I am assuming that you are using a C99 compiler (with support for dynamically sized arrays). The problem in your code is that at the time when the compilers sees your variable declaration it cannot know how many elements there are in the array (I am also assuming here, from the compiler error that length … Read more
[*] (Background: I have some experience implementing C and C++ compilers.) Variable-length arrays in C99 were basically a misstep. In order to support VLAs, C99 had to make the following concessions to common sense: sizeof x is no longer always a compile-time constant; the compiler must sometimes generate code to evaluate a sizeof-expression at runtime. … Read more