Segmentation fault

Code in my DataBase.cpp file:

Code:

#include "DataBase.h"

#include <sqlite3.h>
#include <string.h>
#include <wx/msgdlg.h>


bool CanClose(void)
{
    sqlite3 *Sqlite;
    sqlite3_stmt *sqlstmt;
    char *result;
    if(sqlite3_open("SysConfig",&Sqlite)==SQLITE_OK)
    {
        sqlite3_prepare(Sqlite,"SELECT config_value FROM configuration WHERE config_id = 1;",-1,&sqlstmt,NULL);
        sqlite3_step(sqlstmt);
        result = (char*)sqlite3_column_text(sqlstmt,0);
        sqlite3_close(Sqlite);
        if(strcmp(result,"YES")==1)    //Error Here
            return true;
        else
            return false;
    }
    else
    {
        wxMessageBox(_("Cannot Find System File!"),_("Error!"));
        sqlite3_close(Sqlite);
        return false;
    }
}

My program was behaving abruptly..
When I started debuging the line indicated above (line 19) is giving some error as

program recieved signal SIGSEGV, Segmentation fault.

further dissasembly of the statement show error at a assembly instruction

call 0x80500b0 <strcmp@plt>

Please Help.

I am using CodeBlocks with GCC in linux

Well since I haven't used much sqlite I don't see where your mistake is, but since the error means you are accessing memory you shouldn't be then result probably isn't what you think it is. Have you tried just displaying this variable to the screen to see what its value is?

Sorry if I am way off base but it seems like you set the pointer to point to a memory position then you close that memory position right after. If the compiler isn't allowed to acces that memory after the close function then the strcmp() probably creates a seg fault. Maybe set an int to recieve the return of strcmp then close the file then do a return based on the int.

Three problems:
First, you are using SQLite - a C library. There are C++ wrappers. I strongly recommend you get one.
Second, result may be NULL. Obviously comparing a NULL pointer will get you nowhere except into undefined land (probably crash).
Third, who owns the memory returned by sqlite3_column_text? You? Or Sqlite? What happens when you call close? Does it free the memory? Or do you have to?

Originally Posted by Elysia

Three problems:
First, you are using SQLite - a C library. There are C++ wrappers. I strongly recommend you get one.
Second, result may be NULL. Obviously comparing a NULL pointer will get you nowhere except into undefined land (probably crash).
Third, who owns the memory returned by sqlite3_column_text? You? Or Sqlite? What happens when you call close? Does it free the memory? Or do you have to?

1. I will surely look for it although I thought that a c library should work well with c++. But still as you have told me. A c++ library with classes in it would be much better to use. Thanks for this.

2. You are right. The result

result = (char*)sqlite3_column_text(sqlstmt,0);

is throwing out is NULL. (I must have look for it before).

3. I Changed the code and closed the DB after I have check for the string but it didn't worked...(I did it before step 2)

Code:

bool res=(strcmp(result,"YES")==1);
        sqlite3_close(Sqlite);
        return res;

I will surely look for the SQLite C++ version. But Still Can you tell me why the above mentioned statement is returning a NULL. Though all the code is correctly carved.

Putting Some More checks revealed that sqlite3_prepare() is returning a SQLITE_ERROR where
#define SQLITE_ERROR 1 /* SQL error or missing database */

Originally Posted by C_programmer.C

Code:

if(strcmp(result,"YES")==1)    //Error Here

strcmp() returns 0 when the strings are equal. 1 is returned when the compared string is "greater." look at the docs to know what that means. I'm not sure if that's what you intended

I suggest reading about the return value meanings.

strcmp - C++ Reference

Also, suggest checking for NULL before doing strcmp.

Tim S.

Originally Posted by stahta01

I suggest reading about the return value meanings.

strcmp - C++ Reference

Also, suggest checking for NULL before doing strcmp.

Tim S.

Originally Posted by Elkvis

strcmp() returns 0 when the strings are equal. 1 is returned when the compared string is "greater." look at the docs to know what that means. I'm not sure if that's what you intended

please read my previous post. The talk about return value of strcmp comes later. First I have to resolve the problem that is occurring in sqlite3_prepare() statement.

By the way, why are you not using sqlite3_prepare_v2?

I have used it! Same result....

Let's just confirm this: when you only call sqlite3_prepare_v2, you get the error? I note that your attempt to use sqlite3_column_text is wrong: once you use sqlite3_close, the memory location is invalidated. You should copy the result first, e.g., into a std::string, perhaps calling sqlite3_column_bytes() to find out the size of the result first.

I think it would be good if I post the new DataBase.cpp

Code:

#include "DataBase.h"

#include <sqlite3.h>
#include <string.h>
#include <wx/msgdlg.h>


bool CanClose(void)
{
    sqlite3 *Sqlite;
    sqlite3_stmt *sqlstmt;
    char *result;
    const char*tal;
    bool res;
    if(sqlite3_open("SysConfig",&Sqlite)==SQLITE_OK)
    {
        int i=sqlite3_prepare_v2(Sqlite,"SELECT * FROM configuration WHERE config_id = 1;",100,&sqlstmt,&tal);
        if(i==SQLITE_OK)
        if(sqlite3_step(sqlstmt)==SQLITE_ROW)
        {
            result = (char*)sqlite3_column_text(sqlstmt,0);
            wxString str;
            wxMessageBox(str.FromAscii(result));
            res=(strcmp(result,"YES")==1);
            sqlite3_close(Sqlite);
            return res;
        }
        else wxMessageBox(_("Statement Execution Error!"),_("Error!"));
        else wxMessageBox(_("Cannot Prepare Statement"));

        return 0;
    }
    else
    {
        wxMessageBox(_("Cannot Find System File!"),_("Error!"));
        sqlite3_close(Sqlite);
        return false;
    }
}

now here I am getting that message box with "Cannot Prepare Statement"....
I copied the sql statement and pasted in sqliteman which gave me the desired result with out any error.
further more sqlite3_prepare_v2 is returning SQLITE_ERROR...

Perhaps you can print actual error codes instead of the vague and uninformative "it doesn't work"
Result Codes

> res=(strcmp(result,"YES")==1);
As already mentioned, strcmp() does NOT return 1 when the strings match.
In fact, it doesn't return 1 at all (except for some special circumstances).

If you have
res = strcmp(result,"YES");
then you have
if ( res == 0 )
if ( res < 0 )
if ( res > 0 )
There is no == 1 test!

Read the manual page for everything you're using. If you're this badly wrong on something simple like strcmp(), then there's no hope for you when it comes to SQLite.

Well! the talk of what strcmp returns would come far after I get some success in properly executing sqlite3_prepare_v2 then sqlite3_step and then strcmp. And then would be the time I should google for the return values of strcmp or some other basic functions.
And the reason I have made this mistake is that I am returning to C/C++ after a time span of about 10 months. I was busy with development in C#, and you might know that there is no concept of strcmp and its return values in C#......