自学教程：C++ pwrite函数代码示例

int keydiv_dtable::create(int dfd, const char * name, const params & config, dtype::ctype key_type){	int r, kdd_dfd, meta;	divider_list dividers;	const dtable_factory * base;	params base_config;		kddtable_header header;	header.magic = KDDTABLE_MAGIC;	header.version = KDDTABLE_VERSION;	switch(key_type)	{		case dtype::UINT32:			header.key_type = 1;			r = load_dividers<int, uint32_t>(config, 0, &dividers);			break;		case dtype::DOUBLE:			header.key_type = 2;			r = load_dividers<float, double>(config, 0, &dividers);			break;		case dtype::STRING:			header.key_type = 3;			r = load_dividers<istr, istr>(config, 0, &dividers);			break;		case dtype::BLOB:			header.key_type = 4;			r = load_dividers<blob, blob>(config, 0, &dividers, true);			break;		default:			return -EINVAL;	}	header.dt_count = dividers.size() + 1;	/* make sure we don't overflow the header field */	if(header.dt_count != dividers.size() + 1)		return -EINVAL;		base = dtable_factory::lookup(config, "base");	if(!base)		return -EINVAL;	if(!config.get("base_config", &base_config, params()))		return -EINVAL;		r = mkdirat(dfd, name, 0755);	if(r < 0)		return r;	kdd_dfd = openat(dfd, name, O_RDONLY);	if(kdd_dfd < 0)	{		unlinkat(dfd, name, AT_REMOVEDIR);		return kdd_dfd;	}		for(uint32_t i = 0; i < header.dt_count; i++)	{		char name[32];		sprintf(name, "kdd_data.%u", i);		r = base->create(kdd_dfd, name, base_config, key_type);		if(r < 0)			goto fail;	}		meta = openat(kdd_dfd, "kdd_meta", O_WRONLY | O_CREAT, 0644);	if(meta < 0)	{		r = meta;		goto fail;	}	r = pwrite(meta, &header, sizeof(header), 0);	close(meta);	if(r != sizeof(header))		goto fail;	close(kdd_dfd);	return 0;	fail:	close(kdd_dfd);	util::rm_r(dfd, name);	return (r < 0) ? r : -1;}

voidruntime
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