描述
sqlite3_config功能用于对SQLite进行全局配置更改，以便将SQLite调整为应用程序的特定需求。建议大多数应用程序使用默认配置，因此通常不需要此函数。它提供用于支持具有不寻常需求的罕见应用程序。
C / C ++语法
int sqlite3_config(int, ...); |
PB语法
FUNCTION sqlite3_config ( _ BYVAL op AS LONG, _ OPTIONAL BYREF ANY, BYREF ANY, BYREF ANY, BYREF ANY, _ BYREF ANY, BYREF ANY, BYREF ANY, BYREF ANY, BYREF ANY, _ BYREF ANY, BYREF ANY, BYREF ANY, BYREF ANY, BYREF ANY, _ BYREF ANY, BYREF ANY _ ) AS LONG |
参数
op
[in]一个整数配置选项，用于确定要配置SQLite的什么属性。后续参数因第一个参数中的配置选项而异。
返回值
设置配置选项时，sqlite3_config返回SQLITE_OK。如果该选项未知或SQLite无法设置该选项，则该函数返回非零错误代码。
备注
sqlite3_config功能不是线程安全的。应用程序必须确保在运行sqlite3_config时，其他线程不会调用其他SQLite 函数。此外，sqlite3_config只能在库初始化之前使用sqlite3_initialize或关闭sqlite3_shutdown后调用。如果sqlite3_config在sqlite3_initialize之后和sqlite3_shutdown之前调用，那么它将返回SQLITE_MISUSE。但是请注意，sqlite3_config可以作为应用程序定义的sqlite3_os_init的一部分进行调用。
C ++实现代码
/*
** This API allows applications to modify the global configuration of
** the SQLite library at run-time.
**
** This function should only be called when there are no outstanding
** database connections or memory allocations. This function is not
** threadsafe. Failure to heed these warnings can lead to unpredictable
** behavior.
*/
SQLITE_API int sqlite3_config(int op, ...){
va_list ap;
int rc = SQLITE_OK;
/* sqlite3_config() shall return SQLITE_MISUSE if it is invoked while
** the SQLite library is in use. */
if( sqlite3GlobalConfig.isInit ) return SQLITE_MISUSE_BKPT;
va_start(ap, op);
switch( op ){
/* Mutex configuration options are only available in a threadsafe
** compile.
*/
#if defined(SQLITE_THREADSAFE) && SQLITE_THREADSAFE>0
case SQLITE_CONFIG_SINGLETHREAD: {
/* Disable all mutexing */
sqlite3GlobalConfig.bCoreMutex = 0;
sqlite3GlobalConfig.bFullMutex = 0;
break;
}
case SQLITE_CONFIG_MULTITHREAD: {
/* Disable mutexing of database connections */
/* Enable mutexing of core data structures */
sqlite3GlobalConfig.bCoreMutex = 1;
sqlite3GlobalConfig.bFullMutex = 0;
break;
}
case SQLITE_CONFIG_SERIALIZED: {
/* Enable all mutexing */
sqlite3GlobalConfig.bCoreMutex = 1;
sqlite3GlobalConfig.bFullMutex = 1;
break;
}
case SQLITE_CONFIG_MUTEX: {
/* Specify an alternative mutex implementation */
sqlite3GlobalConfig.mutex = *va_arg(ap, sqlite3_mutex_methods*);
break;
}
case SQLITE_CONFIG_GETMUTEX: {
/* Retrieve the current mutex implementation */
*va_arg(ap, sqlite3_mutex_methods*) = sqlite3GlobalConfig.mutex;
break;
}
#endif
case SQLITE_CONFIG_MALLOC: {
/* Specify an alternative malloc implementation */
sqlite3GlobalConfig.m = *va_arg(ap, sqlite3_mem_methods*);
break;
}
case SQLITE_CONFIG_GETMALLOC: {
/* Retrieve the current malloc() implementation */
if( sqlite3GlobalConfig.m.xMalloc==0 ) sqlite3MemSetDefault();
*va_arg(ap, sqlite3_mem_methods*) = sqlite3GlobalConfig.m;
break;
}
case SQLITE_CONFIG_MEMSTATUS: {
/* Enable or disable the malloc status collection */
sqlite3GlobalConfig.bMemstat = va_arg(ap, int);
break;
}
case SQLITE_CONFIG_SCRATCH: {
/* Designate a buffer for scratch memory space */
sqlite3GlobalConfig.pScratch = va_arg(ap, void*);
sqlite3GlobalConfig.szScratch = va_arg(ap, int);
sqlite3GlobalConfig.nScratch = va_arg(ap, int);
break;
}
case SQLITE_CONFIG_PAGECACHE: {
/* Designate a buffer for page cache memory space */
sqlite3GlobalConfig.pPage = va_arg(ap, void*);
sqlite3GlobalConfig.szPage = va_arg(ap, int);
sqlite3GlobalConfig.nPage = va_arg(ap, int);
break;
}
case SQLITE_CONFIG_PCACHE: {
/* no-op */
break;
}
case SQLITE_CONFIG_GETPCACHE: {
/* now an error */
rc = SQLITE_ERROR;
break;
}
case SQLITE_CONFIG_PCACHE2: {
/* Specify an alternative page cache implementation */
sqlite3GlobalConfig.pcache2 = *va_arg(ap, sqlite3_pcache_methods2*);
break;
}
case SQLITE_CONFIG_GETPCACHE2: {
if( sqlite3GlobalConfig.pcache2.xInit==0 ){
sqlite3PCacheSetDefault();
}
*va_arg(ap, sqlite3_pcache_methods2*) = sqlite3GlobalConfig.pcache2;
break;
}
#if defined(SQLITE_ENABLE_MEMSYS3) || defined(SQLITE_ENABLE_MEMSYS5)
case SQLITE_CONFIG_HEAP: {
/* Designate a buffer for heap memory space */
sqlite3GlobalConfig.pHeap = va_arg(ap, void*);
sqlite3GlobalConfig.nHeap = va_arg(ap, int);
sqlite3GlobalConfig.mnReq = va_arg(ap, int);
if( sqlite3GlobalConfig.mnReq<1 ){
sqlite3GlobalConfig.mnReq = 1;
}else if( sqlite3GlobalConfig.mnReq>(1<<12) ){
/* cap min request size at 2^12 */
sqlite3GlobalConfig.mnReq = (1<<12);
}
if( sqlite3GlobalConfig.pHeap==0 ){
/* If the heap pointer is NULL, then restore the malloc implementation
** back to NULL pointers too. This will cause the malloc to go
** back to its default implementation when sqlite3_initialize() is
** run.
*/
memset(&sqlite3GlobalConfig.m, 0, sizeof(sqlite3GlobalConfig.m));
}else{
/* The heap pointer is not NULL, then install one of the
** mem5.c/mem3.c methods. If neither ENABLE_MEMSYS3 nor
** ENABLE_MEMSYS5 is defined, return an error.
*/
#ifdef SQLITE_ENABLE_MEMSYS3
sqlite3GlobalConfig.m = *sqlite3MemGetMemsys3();
#endif
#ifdef SQLITE_ENABLE_MEMSYS5
sqlite3GlobalConfig.m = *sqlite3MemGetMemsys5();
#endif
}
break;
}
#endif
case SQLITE_CONFIG_LOOKASIDE: {
sqlite3GlobalConfig.szLookaside = va_arg(ap, int);
sqlite3GlobalConfig.nLookaside = va_arg(ap, int);
break;
}
/* Record a pointer to the logger funcction and its first argument.
** The default is NULL. Logging is disabled if the function pointer is
** NULL.
*/
case SQLITE_CONFIG_LOG: {
/* MSVC is picky about pulling func ptrs from va lists.
** http://support.microsoft.com/kb/47961
** sqlite3GlobalConfig.xLog = va_arg(ap, void(*)(void*,int,const char*));
*/
typedef void(*LOGFUNC_t)(void*,int,const char*);
sqlite3GlobalConfig.xLog = va_arg(ap, LOGFUNC_t);
sqlite3GlobalConfig.pLogArg = va_arg(ap, void*);
break;
}
case SQLITE_CONFIG_URI: {
sqlite3GlobalConfig.bOpenUri = va_arg(ap, int);
break;
}
default: {
rc = SQLITE_ERROR;
break;
}
}
va_end(ap);
return rc;
}