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SQLLite (四)：sqlite3_prepare_v2,sqlite3_step

2020-07-04 Sqlite 前端之家

前端之家收集整理的这篇文章主要介绍了SQLLite (四)：sqlite3_prepare_v2,sqlite3_step，前端之家小编觉得挺不错的，现在分享给大家，也给大家做个参考。

如果既不想写回调函数，又想避免 sqlite3_get_table之后麻烦的一维数组遍历，那么利用sqlite3_prepare_v2执行sql select语句，让后sqlite3_step遍历select执行的返回结果是一个非常方便的solution. 当然，你必须要明白sqlite3_prepare_v2不仅仅能够执行table的query selection，也能方便地进行sql Delete,Insert,Update等其他一些操作。它能帮你把sql语句的执行操作变的更加优雅。

[cpp]view plaincopy 
    
 intsqlite3_prepare_v2(
 sqlite3*db,<spanstyle="color:#009900;">/*Databasehandle*/</span>
 constchar*zsql,<spanstyle="color:#009900;">/*sqlstatement,UTF-8encoded*/</span>
 intnByte,0); background-color:inherit">/*Maximumlengthofzsqlinbytes.*/</span>
 sqlite3_stmt**ppStmt,0); background-color:inherit">/*OUT:Statementhandle*/</span>
 char**pzTail<spanstyle="color:#009900;">/*OUT:Pointertounusedportionofzsql*/</span>
 );

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sqlite3_step(sqlite3_stmt*);

下面以一段iOS中的selection查询为例说明二者的用法：

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-(void)InitializeFilesTable

{
char*query="SELECT*FROM[FileObjects]";
sqlite3_stmt*stmt;
intresult=sqlite3_prepare_v2(mDatabase,query,-1,&stmt,NULL);
if(sqlITE_OK!=result)
{
sqlite3_finalize(stmt);
<spanstyle="color:#009900;">//Thetablehasnotbeencreated.Mostlikely,thisisthefirsttimewecreatethedatabase.
//Therefore,createalltablesinit</span>
char*sql="CreateTABLE[FileObjects]([FileId]VARCHAR(128),[FileExt]VARCHAR(128),[FileName]VARCHAR(128),[FileUrl]VARCHAR(128),[FileType]INT);";<spanstyle="color:#009900;">//NOXLATE</span>
char*errMsg;
result=sqlite3_exec(mDatabase,sql,NULL,&errMsg);
}
else
//SelectreturnsOK,initializethememorymodelfromtheresult</span>
NSMutableDictionary*files=[NSMutableDictionarynew];
while(sqlite3_step(stmt)==sqlITE_ROW)
FileObject*file=[FileObjectnew];
char*str=(char*)sqlite3_column_text(stmt,0);
file.FileId=str?[[NSStringalloc]initWithUTF8String:str]:@"";
str=( file.FileExt=str?[[NSStringalloc]initWithUTF8String:str]:@"";
str=( file.FileName=str?[[NSStringalloc]initWithUTF8String:str]:@"";
file.FileUrl=str?[[NSStringalloc]initWithUTF8String:str]:@"";
file.FileType=sqlite3_column_int(stmt,4);
[filessetObject:fileforKey:file.FileId];
[mFilessetDictionary:files];
}