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Flexible array member
open-in-new
<p><a href="/facts/C_/Ky2No763">C</a> <a href="/facts/Struct_(C_programming_language)/mmhEWucA">struct</a> data types may end with a flexible <a href="/facts/Array_data_structure/BKGvF8AM">array</a> member with no specified size: </p> struct vectord { short 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 }; <p>Typically, such structures serve as the header in a larger, <a href="/facts/C_dynamic_memory_allocation/llutVVlp">variable memory allocation</a>: </p> struct vectord *vector = malloc(...); vector->len = ...; for (int i = 0; i < vector->len; i++) vector->arr[i] = ...; // transparently uses the right type (double)