Read an entire file into a buffer (without race conditions or seeking).

read_entire_file.c

void* fread_all(FILE* file, size_t* out_size) {
    const size_t BLOCK_SIZE = 32 * 1024;
    const size_t MEDIUM_SIZE = 10 * 1024 * 1024;

    *out_size = 0;

    size_t cap = 0;
    char* data = NULL;

    while (1) {
        if (*out_size + BLOCK_SIZE > cap) {
            if (cap > MEDIUM_SIZE) {
                cap = (cap * 3) / 2;
            } else if (cap < BLOCK_SIZE) {
                cap = BLOCK_SIZE;
            } else {
                cap *= 2;
            }

            void* new_data = realloc(data, cap);
            if (!new_data) {
                *out_size = 0;
                free(data);
                return NULL;
            }
            data = new_data;
        }

        size_t read = fread(data + *out_size, 1, BLOCK_SIZE, file);
        *out_size += read;
        if (read < BLOCK_SIZE) {
            if (ferror(file)) {
                *out_size = 0;
                free(data);
                return NULL;
            } else {
                return data;
            }
        }
    }
}