C++、SQLite - 指向字符串指针的指针

发布于 2024-11-03 12:05:15 字数 974 浏览 1 评论 0原文

我使用 C++ 和 SQLite3（使用 Microsoft Visual C++ 2008），希望从数据库中读取一个值并将其存储在一个变量中以供使用。 select 语句工作正常，但每次我查看回调函数并尝试从 char **argv 读取值时，我“仅”得到内存地址或数据库中该值的第一个 ASCII 字符。我做错了什么？这是回调函数：

static int callback(void *pArg, int argc, char **argv, char **azColName)
{
fprintf(f, "Callback aufgerufen!\n");
int i;  

for(i=0; i<argc; i++)
{
    fprintf(f, azColName[i]);
    fprintf(f, " = ");
    if(argv[i]){
        fprintf(f, argv[i]);
        //unsigned int x = argv[i];
    }

    else
        fprintf(f, "NULL");
        fprintf(f, "\n");
 }
fprintf(f, "\n");
return 0;
}

我在没有回调函数的情况下尝试了它，但我再次得到了相同的结果，并且我尝试了不同的方法将值存储在变量中。

while (sqlite3_step(stmt) == SQLITE_ROW) 
{
    fprintf(f, "%s\n", sqlite3_column_text(stmt, 0));
//const unsigned char *c = sqlite3_column_text(stmt, 0);
fprintf(f, "%u\n", sqlite3_column_int(stmt, 0));
//unsigned int z = *sqlite3_column_int(stmt, 0);

stmt_count++;
}

是否可能无法访问该值或将其存储在变量中？

原文

I work with C++ and SQLite3 (with Microsoft Visual C++ 2008) and would like to read a value from my database and store it in a variable to work with it on.
The select statement works fine, but every time I viewed the callback function and try to read the value from char **argv, I get "only" the memory address, or the first ASCII character of the value, which is in the database. What am I doing wrong?
Here is the callback function:

static int callback(void *pArg, int argc, char **argv, char **azColName)
{
fprintf(f, "Callback aufgerufen!\n");
int i;  

for(i=0; i<argc; i++)
{
    fprintf(f, azColName[i]);
    fprintf(f, " = ");
    if(argv[i]){
        fprintf(f, argv[i]);
        //unsigned int x = argv[i];
    }

    else
        fprintf(f, "NULL");
        fprintf(f, "\n");
 }
fprintf(f, "\n");
return 0;
}

I tried it without the callback function, but again I get the same result and I've tried different ways to store the value in a variable.

while (sqlite3_step(stmt) == SQLITE_ROW) 
{
    fprintf(f, "%s\n", sqlite3_column_text(stmt, 0));
//const unsigned char *c = sqlite3_column_text(stmt, 0);
fprintf(f, "%u\n", sqlite3_column_int(stmt, 0));
//unsigned int z = *sqlite3_column_int(stmt, 0);

stmt_count++;
}

Is it perhaps not possible to access the value or to store it in a variable?

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涫野音 2024-11-10 12:05:15

我不明白为什么你需要回调 - 这应该有效（取决于数据的大小）：

char myvalue[100];
while (sqlite3_step(stmt) == SQLITE_ROW) 
{
    strcpy( myvalue, (const char *) sqlite3_column_text(stmt, 0) );
    // do something with myvalue
    stmt_count++;
}

I don't see why you need a callback - this should work (depending on the size of the data):

char myvalue[100];
while (sqlite3_step(stmt) == SQLITE_ROW) 
{
    strcpy( myvalue, (const char *) sqlite3_column_text(stmt, 0) );
    // do something with myvalue
    stmt_count++;
}

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