在finalize / close期间,sqlite3_column_text返回的数据被破坏

我不确定这里发生了什么,但我发现在finalize / close sqlite阶段,sqlite3_column_text返回的数据正在被更改.

// rc not handled in this abbreviated code

  sqlite3 *db;
  sqlite3_stmt *stmt;
  char * sql;

  const char * tail;
  int rc;

  char * dbName = "C:\\db\\myblobs.db";
  int myIndex = 0;

  char * myLocation1;
  string myLocation2;   

  rc = sqlite3_open(dbName,&db);

  sql = "SELECT location FROM blobs WHERE key = ?";
  rc = sqlite3_prepare(db,sql,strlen(sql),&stmt,&tail);
  sqlite3_bind_int(stmt,1,myIndex);
  rc = sqlite3_step(stmt);

  myLocation1 = (char*)sqlite3_column_text(stmt,0);
  myLocation2 = (char*)sqlite3_column_text(stmt,0);

  // can process myLocation1 & myLocation2 fine here

  sqlite3_finalize(stmt); // data myLocation1 points to get corrupted
  sqlite3_close(db);      // data myLocation2 points to gets further corrupted

问题与myLocation1有关.它指向的数据很好,直到它到达sqlite3_finalize和sqlite3_close语句.然而,mylocation2保持不变.所以不确定这里发生了什么.执行sqlite3_close(db)后,myLocation1在Visual Studio 2010中被标识为“Bad Ptr”.

任何帮助最受赞赏.

从 fine manual：

const unsigned char *sqlite3_column_text(sqlite3_stmt*,int iCol);
[…]
The pointers returned are valid until a type conversion occurs as described above,or until sqlite3_step() or sqlite3_reset() or sqlite3_finalize() is called.

因此,只要调用 sqlite3_finalize,sqlite3_column_text的返回值就会变为无效,而myLocation1和myLocation2指针指向垃圾.

如果在调用 sqlite3_finalize之后需要这些字符串,则必须将它们复制到您控制的内存中.实际上,由于在类型转换发生之前有效,因此应立即复制它们并仅使用(char *)sqlite3_column_text(stmt,0);而你正在制作自己的副本.

在finalize / close期间,sqlite3_column_text返回的数据被破坏

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