c / expert
Snippet
Flexible Array Members (FAMs)
Flexible Array Members (introduced in C99) allow a structure to end with an unsized array. This technique enables a single heap allocation to contain both the metadata header and the variable-length payload, improving cache locality and reducing allocation overhead compared to storing a separate pointer.
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#include <stdio.h>#include <stdlib.h>#include <stdint.h>struct DynamicBuffer {size_t size;uint8_t data[]; // Flexible array member};int main() {size_t n = 1024;// Allocate header + n bytes for the arraystruct DynamicBuffer *buf = malloc(sizeof(struct DynamicBuffer) + n);if (!buf) return 1;buf->size = n;for (size_t i = 0; i < n; i++) buf->data[i] = (uint8_t)(i % 256);printf("Size: %zu, First element: %u\n", buf->size, buf->data[0]);free(buf);return 0;}
Breakdown
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uint8_t data[];
The flexible array member must be the last element of the struct and has no specified size.
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malloc(sizeof(struct DynamicBuffer) + n);
Memory is allocated for the base struct size plus the desired number of array elements.