An array parameter uses array notation in a function interface, but C rewrites it to a pointer. The innermost array dimension is therefore lost, and the function operates on the caller’s elements rather than a copied array. section 6.1.4 section 11.3.2
Swapping elements through an array parameter
void swap_double(double a[static 2]) { a[0] and a[1] are exchanged; } Calling swap_double(A) changes A directly. The declaration is equivalent in parameter type to a pointer form, while preserving useful array-sized interface notation. section 11.3.2
TAKEAWAY rules:
- Do not use sizeof on an array parameter; it does not retain the array object’s size. section 6.1.4
- Expect only the innermost dimension to rewrite; multidimensional parameters retain subsequent dimensions as pointer-to-array types. section 11.3.2
- Prefer array notation when the parameter represents a non-null array and document its expected length when possible. section 11.3.2
void matrix_mult(size_t n, size_t k, size_t m,
double C[n][m],
double const A[n][k],
double const B[k][m]) {
for (size_t i = 0; i < n; ++i) {
for (size_t j = 0; j < m; ++j) {
C[i][j] = 0.0;
for (size_t l = 0; l < k; ++l) {
C[i][j] += A[i][l]*B[l][j];
}
}
}
}
Matrix multiplication demonstrates array notation for multidimensional parameters, with dimensions supplied before the arrays. section 11.3.2
