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最近在做物联网gateway，需要用到很多c语言知识。近期抽时间来看一下SQLite的源代码，来逐步分析一下人家的各种特性是怎么实现的。
也希望对自己的C代的基本功和提高有一些帮助吧。
代码版本：sqlite-amalgamation-3110100
以后就以这个版本为主要分析过程。
下载地址：http://www.sqlite.org/download.html
说明：一共四个文件，放在新建的VS工程中，既可以启动程序，并且出现SQLite的程序运行窗口，
然后就可以使用各种命令来进行相关的操作了。这个可以参考各种指导。
我这里主要就是分析各种功能是如何实现的。并且对源代码进行相关的说明。
该程序的启动函数是main函数。该函数代码如下：
int SQLITE_CDECL main(int argc,char **argv){
char *zErrMsg = 0;
ShellState data;
const char *zInitFile = 0;
int i;
int rc = 0;
int warnInmemoryDb = 0;
int readStdin = 1;
int nCmd = 0;
char **azCmd = 0;
#if USE_SYSTEM_SQLITE+0!=1
if( strcmp(sqlite3_sourceid(),SQLITE_SOURCE_ID)!=0 ){
utf8_printf(stderr,"SQLite header and source version mismatchn%sn%sn",
sqlite3_sourceid(),SQLITE_SOURCE_ID);
exit(1);
}
#endif
setBinaryMode(stdin);
setvbuf(stderr,_IONBF,0); /* Make sure stderr is unbuffered */
Argv0 = argv[0];
main_init(&data);
stdin_is_interactive = isatty(0);
stdout_is_console = isatty(1);
/* Make sure we have a valid signal handler early,before anything
** else is done.
*/
#ifdef SIGINT
signal(SIGINT,interrupt_handler);
#endif
#ifdef SQLITE_SHELL_DBNAME_PROC
{
/* If the SQLITE_SHELL_DBNAME_PROC macro is defined,then it is the name
** of a C-function that will provide the name of the database file. Use
** this compile-time option to embed this shell program in larger
** applications. */
extern void SQLITE_SHELL_DBNAME_PROC(const char**);
SQLITE_SHELL_DBNAME_PROC(&data.zDbFilename);
warnInmemoryDb = 0;
}
#endif
/* Do an initial pass through the command-line argument to locate
** the name of the database file,the name of the initialization file,
** the size of the alternative malloc heap,
** and the first command to execute.
*/
for(i=1; i<argc; i++){
char *z;
z = argv[i];
if( z[0]!='-' ){
if( data.zDbFilename==0 ){
data.zDbFilename = z;
}else{
/* Excesss arguments are interpreted as SQL (or dot-commands) and
** mean that nothing is read from stdin */
readStdin = 0;
nCmd++;
azCmd = realloc(azCmd,sizeof(azCmd[0])*nCmd);
if( azCmd==0 ){
raw_printf(stderr,"out of memoryn");
exit(1);
}
azCmd[nCmd-1] = z;
}
}
if( z[1]=='-' ) z++;
if( strcmp(z,"-separator")==0
|| strcmp(z,"-nullvalue")==0
|| strcmp(z,"-newline")==0
|| strcmp(z,"-cmd")==0
){
(void)cmdline_option_value(argc,argv,++i);
}else if( strcmp(z,"-init")==0 ){
zInitFile = cmdline_option_value(argc,"-batch")==0 ){
/* Need to check for batch mode here to so we can avoid printing
** informational messages (like from process_sqliterc) before
** we do the actual processing of arguments later in a second pass.
*/
stdin_is_interactive = 0;
}else if( strcmp(z,"-heap")==0 ){
#if defined(SQLITE_ENABLE_MEMSYS3) || defined(SQLITE_ENABLE_MEMSYS5)
const char *zSize;
sqlite3_int64 szHeap;
zSize = cmdline_option_value(argc,++i);
szHeap = integerValue(zSize);
if( szHeap>0x7fff0000 ) szHeap = 0x7fff0000;
sqlite3_config(SQLITE_CONFIG_HEAP,malloc((int)szHeap),(int)szHeap,64);
#endif
}else if( strcmp(z,"-scratch")==0 ){
int n,sz;
sz = (int)integerValue(cmdline_option_value(argc,++i));
if( sz>400000 ) sz = 400000;
if( sz<2500 ) sz = 2500;
n = (int)integerValue(cmdline_option_value(argc,++i));
if( n>10 ) n = 10;
if( n<1 ) n = 1;
sqlite3_config(SQLITE_CONFIG_SCRATCH,malloc(n*sz+1),sz,n);
data.shellFlgs |= SHFLG_Scratch;
}else if( strcmp(z,"-pagecache")==0 ){
int n,++i));
if( sz>70000 ) sz = 70000;
if( sz<0 ) sz = 0;
n = (int)integerValue(cmdline_option_value(argc,++i));
sqlite3_config(SQLITE_CONFIG_PAGECACHE,
(n>0 && sz>0) ? malloc(n*sz) : 0,n);
data.shellFlgs |= SHFLG_Pagecache;
}else if( strcmp(z,"-lookaside")==0 ){
int n,++i));
if( sz<0 ) sz = 0;
n = (int)integerValue(cmdline_option_value(argc,++i));
if( n<0 ) n = 0;
sqlite3_config(SQLITE_CONFIG_LOOKASIDE,n);
if( sz*n==0 ) data.shellFlgs &= ~SHFLG_Lookaside;
#ifdef SQLITE_ENABLE_VFSTRACE
}else if( strcmp(z,"-vfstrace")==0 ){
extern int vfstrace_register(
const char *zTraceName,
const char *zOldVfsName,
int (*xOut)(const char*,void*),
void *pOutArg,
int makeDefault
);
vfstrace_register("trace",(int(*)(const char*,void*))fputs,stderr,1);
#endif
#ifdef SQLITE_ENABLE_MULTIPLEX
}else if( strcmp(z,"-multiplex")==0 ){
extern int sqlite3_multiple_initialize(const char*,int);
sqlite3_multiplex_initialize(0,1);
#endif
}else if( strcmp(z,"-mmap")==0 ){
sqlite3_int64 sz = integerValue(cmdline_option_value(argc,++i));
sqlite3_config(SQLITE_CONFIG_MMAP_SIZE,sz);
}else if( strcmp(z,"-vfs")==0 ){
sqlite3_vfs *pVfs = sqlite3_vfs_find(cmdline_option_value(argc,++i));
if( pVfs ){
sqlite3_vfs_register(pVfs,1);
}else{
utf8_printf(stderr,"no such VFS: "%s"n",argv[i]);
exit(1);
}
}
}
if( data.zDbFilename==0 ){
#ifndef SQLITE_OMIT_MEMORYDB
data.zDbFilename = ":memory:";
warnInmemoryDb = argc==1;
#else
utf8_printf(stderr,"%s: Error: no database filename specifiedn",Argv0);
return 1;
#endif
}
data.out = stdout;
/* Go ahead and open the database file if it already exists. If the
** file does not exist,delay opening it. This prevents empty database
** files from being created if a user mistypes the database name argument
** to the sqlite command-line tool.
*/
if( access(data.zDbFilename,0)==0 ){
open_db(&data,0);
}
/* Process the initialization file if there is one. If no -init option
** is given on the command line,look for a file named ~/.sqliterc and
** try to process it.
*/
process_sqliterc(&data,zInitFile);
/* Make a second pass through the command-line argument and set
** options. This second pass is delayed until after the initialization
** file is processed so that the command-line arguments will override
** settings in the initialization file.
*/
for(i=1; i<argc; i++){
char *z = argv[i];
if( z[0]!='-' ) continue;
if( z[1]=='-' ){ z++; }
if( strcmp(z,"-init")==0 ){
i++;
}else if( strcmp(z,"-html")==0 ){
data.mode = MODE_Html;
}else if( strcmp(z,"-list")==0 ){
data.mode = MODE_List;
}else if( strcmp(z,"-line")==0 ){
data.mode = MODE_Line;
}else if( strcmp(z,"-column")==0 ){
data.mode = MODE_Column;
}else if( strcmp(z,"-csv")==0 ){
data.mode = MODE_Csv;
memcpy(data.colSeparator,",2);
}else if( strcmp(z,"-ascii")==0 ){
data.mode = MODE_Ascii;
sqlite3_snprintf(sizeof(data.colSeparator),data.colSeparator,
SEP_Unit);
sqlite3_snprintf(sizeof(data.rowSeparator),data.rowSeparator,
SEP_Record);
}else if( strcmp(z,"-separator")==0 ){
sqlite3_snprintf(sizeof(data.colSeparator),
"%s",cmdline_option_value(argc,++i));
}else if( strcmp(z,"-newline")==0 ){
sqlite3_snprintf(sizeof(data.rowSeparator),"-nullvalue")==0 ){
sqlite3_snprintf(sizeof(data.nullValue),data.nullValue,"-header")==0 ){
data.showHeader = 1;
}else if( strcmp(z,"-noheader")==0 ){
data.showHeader = 0;
}else if( strcmp(z,"-echo")==0 ){
data.echoOn = 1;
}else if( strcmp(z,"-eqp")==0 ){
data.autoEQP = 1;
}else if( strcmp(z,"-stats")==0 ){
data.statsOn = 1;
}else if( strcmp(z,"-scanstats")==0 ){
data.scanstatsOn = 1;
}else if( strcmp(z,"-backslash")==0 ){
/* Undocumented command-line option: -backslash
** Causes C-style backslash escapes to be evaluated in SQL statements
** prior to sending the SQL into SQLite. Useful for injecting
** crazy bytes in the middle of SQL statements for testing and debugging.
*/
data.backslashOn = 1;
}else if( strcmp(z,"-bail")==0 ){
bail_on_error = 1;
}else if( strcmp(z,"-version")==0 ){
printf("%s %sn",sqlite3_libversion(),sqlite3_sourceid());
return 0;
}else if( strcmp(z,"-interactive")==0 ){
stdin_is_interactive = 1;
}else if( strcmp(z,"-batch")==0 ){
stdin_is_interactive = 0;
}else if( strcmp(z,"-heap")==0 ){
i++;
}else if( strcmp(z,"-scratch")==0 ){
i+=2;
}else if( strcmp(z,"-pagecache")==0 ){
i+=2;
}else if( strcmp(z,"-lookaside")==0 ){
i+=2;
}else if( strcmp(z,"-mmap")==0 ){
i++;
}else if( strcmp(z,"-vfs")==0 ){
i++;
#ifdef SQLITE_ENABLE_VFSTRACE
}else if( strcmp(z,"-vfstrace")==0 ){
i++;
#endif
#ifdef SQLITE_ENABLE_MULTIPLEX
}else if( strcmp(z,"-multiplex")==0 ){
i++;
#endif
}else if( strcmp(z,"-help")==0 ){
usage(1);
}else if( strcmp(z,"-cmd")==0 ){
/* Run commands that follow -cmd first and separately from commands
** that simply appear on the command-line. This seems goofy. It would
** be better if all commands ran in the order that they appear. But
** we retain the goofy behavior for historical compatibility. */
if( i==argc-1 ) break;
z = cmdline_option_value(argc,++i);
if( z[0]=='.' ){
rc = do_meta_command(z,&data);
if( rc && bail_on_error ) return rc==2 ? 0 : rc;
}else{
open_db(&data,0);
rc = shell_exec(data.db,z,shell_callback,&data,&zErrMsg);
if( zErrMsg!=0 ){
utf8_printf(stderr,"Error: %sn",zErrMsg);
if( bail_on_error ) return rc!=0 ? rc : 1;
}else if( rc!=0 ){
utf8_printf(stderr,"Error: unable to process SQL "%s"n",z);
if( bail_on_error ) return rc;
}
}
}else{
utf8_printf(stderr,"%s: Error: unknown option: %sn",Argv0,z);
raw_printf(stderr,"Use -help for a list of options.n");
return 1;
}
data.cMode = data.mode;
}
if( !readStdin ){ /* Run all arguments that do not begin with '-' as if they were separate ** command-line inputs,except for the argToSkip argument which contains ** the database filename. */ for(i=0; i<nCmd; i++){ if( azCmd[i][0]=='.' ){ rc = do_meta_command(azCmd[i],&data); if( rc ) return rc==2 ? 0 : rc; }else{ open_db(&data,0); rc = shell_exec(data.db,azCmd[i],&zErrMsg); if( zErrMsg!=0 ){ utf8_printf(stderr,zErrMsg); return rc!=0 ? rc : 1; }else if( rc!=0 ){ utf8_printf(stderr,"Error: unable to process SQL: %sn",azCmd[i]); return rc; } } } free(azCmd); }else{ /* Run commands received from standard input */ if( stdin_is_interactive ){ char *zHome; char *zHistory = 0; int nHistory; printf( "SQLite version %s %.19sn" /*extra-version-info*/ "Enter ".help" for usage hints.n",sqlite3_sourceid() ); if( warnInmemoryDb ){ printf("Connected to a "); printBold("transient in-memory database"); printf(".nUse ".open FILENAME" to reopen on a " "persistent database.n"); } zHome = find_home_dir(); if( zHome ){ nHistory = strlen30(zHome) + 20; if( (zHistory = malloc(nHistory))!=0 ){ sqlite3_snprintf(nHistory,zHistory,"%s/.sqlite_history",zHome); } } if( zHistory ){ shell_read_history(zHistory); } rc = process_input(&data,0); if( zHistory ){ shell_stifle_history(100); shell_write_history(zHistory); free(zHistory); } }else{ rc = process_input(&data,stdin); } } set_table_name(&data,0); if( data.db ){ sqlite3_close(data.db); } sqlite3_free(data.zFreeOnClose); return rc; } （编辑：李大同）
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