Flexible array member
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C struct data types may end with a flexible array member[1] with no specified size:
typedef struct {
size_t len; // there must be at least one other data member
double arr[]; // the flexible array member must be last
// The compiler may reserve extra padding space here, like it can between struct members
} DoubleArray;
Typically, such structures serve as the header in a larger, variable memory allocation:
// see section on size and padding
DoubleArray* darray = malloc(sizeof(DoubleArray) + ... * sizeof(double));
darray->len = ...;
for (int i = 0; i < darray->len; i++) {
darray->arr[i] = ...; // transparently uses the right type (double)
}
