二维 std::vector&lt; std::vector 上的 push_back<char*> &gt; value 使所有值都相同

Question

How can I adding the value in 2D vector std::vector< std::vector<char*> >

I was using this code, but the items result inside the vetore are the same. Whereas the data from the db querying are varied.

std::vector< std::vector<char*> >  results;
char *dataTemp = new char[128];
sqlite3_stmt *statement;
int rc = sqlite3_prepare_v2(m_pDbFile, sql, -1, &statement, 0);
if( rc == SQLITE_OK )
{
    int cols = sqlite3_column_count(statement);
    int result = 0;
    int count = 0;
    while(true)
    {
        result = sqlite3_step(statement);
        if(result == SQLITE_ROW)
        {
            std::vector<char*, std::allocator<char*>> values;
            for(int col = 0; col < cols; col++)
            {
                char* value = (char*)sqlite3_column_text(statement, col);
                values.push_back((char*)sqlite3_column_text(statement, col));
            }
            results.push_back(values);
        }
        else
        {
            break;  
        }
        count++;
    }
    
    sqlite3_finalize(statement);
}

Answer 1

Problem
Pointer (C type string) returned by sqlite3_column_text may be invalidated / reused after subsequent calls to sql APIs. So you should preserve the contents instead of saving the pointer itself.

Solution
Make the following 3 changes in your code.

#include <string>  // 1
...
std::vector< std::vector<std::string> >  results;  // 2
...
            std::vector<std::string> values;  // 3
            for(int col = 0; col < cols; col++)
            {
                const char* value = (char*)sqlite3_column_text(statement, col);  // Optional
                values.push_back(value);  // Optional
            }
...