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Comment by amiga386 | Hacker News Reader

I thought the main advantage had always been the row/column-major order of arrays:

https://en.wikipedia.org/wiki/Row-_and_column-major_order

In short, people solving numerical problems want to write like M[i,j] where i is iterated through on the innermost loop and j is iterated through on the outermost loop... and if the language works in sympathy with them and gets good cache-coherence, that's great, but if the language works against them and would make them write M[j,i] to get the same performance, they don't like it, so they keep writing M[i,j] and let the slowness be the other language's problem.

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Nah, that is mostly about keeping the ordering in mind when iterating (e.g. do you iterate first over innermost or outermost index?). And there are algorithms such as (naive) matrix multiplication where the correct order for one matrix is the wrong for the other one, so plus ca change.

But speaking of arrays, one definitive advantage of Fortran is that it has built-in multidimensional arrays in the language. Which is very nice when writing code that needs them. In C many people resort to the Fischer-Price My First Multidimensional Array implementation where they allocate each row separately, which is of course horrible. (In C++ you can use libraries like Eigen or Armadillo which use expression templates and operator overloading to have sensible multidimensional array support even if it isn't built-in.)

Uh... C does have multidimensional arrays. Writing "int a[5][10]" allocates the same contiguous storage as "int b[50]", and accessing a[3][7] will access the integer at ((char *)a) + 3*sizeof(int[10]) + 7*sizeof(int), which would be the same offset as b[37].

It has to be row-oriented because the language allows you to take the address of each intermediate dimension, e.g. int *c = &a[3] gets you a pointer to the equivalent offset of b[30], and legally you can access c[0] through to c[9]. Accessing c[10] would be equivalent to a[4][0] and compilers will let you do it, but I think it's officially undefined behaviour?

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