c - 将 sqlite3_column_text() 返回到文字字符串

Question

我有以下疑问:

考虑从 sqlite 数据库中选择下表:

id | label
1  | P1
1  | P2
1  | P3
1  | P4

我运行以下测试代码:

const unsigned char * new1;
const unsigned char * new2;
const unsigned char * new3;
const unsigned char * new4;

sqlite3_step(stmt);
new1=sqlite3_column_text(stmt,1);

sqlite3_step(stmt);
new2=sqlite3_column_text(stmt,1);

sqlite3_step(stmt);
new3=sqlite3_column_text(stmt,1);

sqlite3_step(stmt);
new4=sqlite3_column_text(stmt,1);

printf("%s\n%s\n%s\n%s\n",new1,new2,new3,new4);
printf("%p\n%p\n%p\n%p\n",new1,new2,new3,new4);

我得到:

P4
P4
P4
P4
0x1d5b7f8
0x1d5b7f8
0x1d5b7f8
0x1d5b7f8

我要打印

P1
P2
P3
P4
Address1
Address2
Address3
Address4

有什么方法可以仅使用字符串文字来打印此内容，而不使用缓冲区 const char value[N];、strcpy 等...？

Answer 1

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. The memory space used to hold strings and BLOBs is freed automatically.

除非您在每个 sqlite3_column_text 之后执行 printf(即使如此，地址仍然相同)，否则您需要制作副本。