Problem with a pointer ( non qt question )

[franco.amato]

Hi to all, sorry in advance if this is not a real qt-related problem, but I have some problem with a c source code, gui is still qt :-).
I'm writing a basic decrypting routine that take a pointer to a const message.
so:

void decryptMessage( char* text, const char* );
void main()
{
    char* message = new char[1143];
    strcpy_s(message, 1143, "a big encrypted message");
 
    const char* freqLang = "TEOIARNSHLMYUCWDGPFBVKJ";
 
    decryptMessage( message, freqLang );
 
    delete[] message;
    return 0;
}

void decryptMessage( char* text, const char* );
void main()
{
    char* message = new char[1143];
    strcpy_s(message, 1143, "a big encrypted message");

    const char* freqLang = "TEOIARNSHLMYUCWDGPFBVKJ";

    decryptMessage( message, freqLang );

    delete[] message;
    return 0;
}

To copy to clipboard, switch view to plain text mode 

and then some code of the decryptMessage:

/* decryptMessage function */
void decryptMessage( const char *message, const char *freqLang )
{
    char freqLangCrypt[sizeof(freqLang)];
    int freq[TOTAL_LETTER], pos, c, max, maxj;
    pos = c = 0;
 
    for (int i = 0; i < TOTAL_LETTER; i++)
        freq[i] = 0;
 
    //I read the message the first time to create freq[]
    int index = 0;
    while( (c = message[index]) != '\0' )
    {
       // CODE CODE 
    } // UNTIL NOW I CAN SEE THE POINTER TO MESSAGE
 
    while( (c = message[index]) != '\0' ) // <---  I CAN NOT SEE THE POINTER TO MESSAGE ANYMORE
    {
       //CODE
    }//while
  // MORE CODE
}

/* decryptMessage function */
void decryptMessage( const char *message, const char *freqLang )
{
    char freqLangCrypt[sizeof(freqLang)];
    int freq[TOTAL_LETTER], pos, c, max, maxj;
    pos = c = 0;

    for (int i = 0; i < TOTAL_LETTER; i++)
        freq[i] = 0;
    
    //I read the message the first time to create freq[]
    int index = 0;
    while( (c = message[index]) != '\0' )
    {
       // CODE CODE 
    } // UNTIL NOW I CAN SEE THE POINTER TO MESSAGE

    while( (c = message[index]) != '\0' ) // <---  I CAN NOT SEE THE POINTER TO MESSAGE ANYMORE
    {
       //CODE
    }//while
  // MORE CODE
}

To copy to clipboard, switch view to plain text mode 

I don't understand why the pointer to message disappear (I don't delete it).
Passing it to the routine it should stay visible until the routine returns.
I hope to get help.
Regards,

[Zlatomir]

My guess is that index get to the range in the first loop, and for the second loop is out of range.

Another possible mistake is that you closed one bracket too early, so check that you didn't end the function definition before you want to.

And share more info about how you can't see the pointer, it's an compile error, a run-time error, a syntax highlight error? If you don't provide information we can only guess.

[franco.amato]

My guess is that index get to the range in the first loop, and for the second loop is out of range.

Another possible mistake is that you closed one bracket too early, so check that you didn't end the function definition before you want to.

And share more info about how you can't see the pointer, it's an compile error, a run-time error, a syntax highlight error? If you don't provide information we can only guess.

Hi I don't get compiler error. I get en error at runtime and the index has been reset to zero before the last while loop.
I paste here the whole code ( it's a very basic decryption algorithm )

/* decryptMessage function */
void decryptMessage( const char *message, const char *freqLang )
{
    const char *ptr = message;
    char freqLangCrypt[sizeof(freqLang)];
    //printf("sizeof %d", sizeof(freqLang) );
    int freq[TOTAL_LETTER], pos, c, max, maxj;
    pos = c = 0;
 
    //memset((void*)freq, 0, TOTAL_LETTER);
    for (int i = 0; i < TOTAL_LETTER; i++)
        freq[i] = 0;
 
    //I read the message the first time to create freq[]
    int index = 0;
    while( (c = message[index]) != '\0' )
    {
        if (isalpha(c))
        {
            c = toupper(c);
            pos = c - 'A';
            freq[pos] = freq[pos] + 1; //freq[0] = number of 'a' and 'A' in the file
        }
        index++;
    }
 
    //here I create freqLangCrypt[] from freq[]
    //freqLangCrypt[] frequency table of the crypted message 
    for(int i = 0; i < TOTAL_LETTER; i++)
    {
        max = 0;
        maxj = -1;
        //I search the maximum values in freq
        for(int j = 0; j < TOTAL_LETTER; j++)
        {
            if(freq[j] > max)
            {
                max = freq[j];
                maxj = j;
            }
        }//for
        if(maxj > -1)
        {
            freqLangCrypt[i] = maxj + 'A';
            freq[maxj] = 0;
        }
    }//for
 
    //read again the message to decrypt it
    index = 0;
    char *pdest = 0;
    while( (c = ptr[index]) != '\0' )
    {
        if (isalpha(c))
        {    
            c = toupper(c);
            pdest = strchr(freqLangCrypt, c);
            if( pdest != NULL )
            {
                index = (int)(pdest - freqLangCrypt);
                putchar(freqLang[index]);
            }
            else
                putchar(c);
        }//if(isalpha(c))
        else
            putchar(c);
        index++;
    }//while
}//end of decryptMessage

/* decryptMessage function */
void decryptMessage( const char *message, const char *freqLang )
{
    const char *ptr = message;
    char freqLangCrypt[sizeof(freqLang)];
    //printf("sizeof %d", sizeof(freqLang) );
    int freq[TOTAL_LETTER], pos, c, max, maxj;
    pos = c = 0;

    //memset((void*)freq, 0, TOTAL_LETTER);
    for (int i = 0; i < TOTAL_LETTER; i++)
        freq[i] = 0;
    
    //I read the message the first time to create freq[]
    int index = 0;
    while( (c = message[index]) != '\0' )
    {
        if (isalpha(c))
        {
            c = toupper(c);
            pos = c - 'A';
            freq[pos] = freq[pos] + 1; //freq[0] = number of 'a' and 'A' in the file
        }
        index++;
    }

    //here I create freqLangCrypt[] from freq[]
    //freqLangCrypt[] frequency table of the crypted message 
    for(int i = 0; i < TOTAL_LETTER; i++)
    {
        max = 0;
        maxj = -1;
        //I search the maximum values in freq
        for(int j = 0; j < TOTAL_LETTER; j++)
        {
            if(freq[j] > max)
            {
                max = freq[j];
                maxj = j;
            }
        }//for
        if(maxj > -1)
        {
            freqLangCrypt[i] = maxj + 'A';
            freq[maxj] = 0;
        }
    }//for

    //read again the message to decrypt it
    index = 0;
    char *pdest = 0;
    while( (c = ptr[index]) != '\0' )
    {
        if (isalpha(c))
        {    
            c = toupper(c);
            pdest = strchr(freqLangCrypt, c);
            if( pdest != NULL )
            {
                index = (int)(pdest - freqLangCrypt);
                putchar(freqLang[index]);
            }
            else
                putchar(c);
        }//if(isalpha(c))
        else
            putchar(c);
        index++;
    }//while
}//end of decryptMessage

To copy to clipboard, switch view to plain text mode 

and the main:

#define TOTAL_LETTER 26
 
 
void decryptMessage( char* text, const char* );
 
int _tmain(int argc, _TCHAR* argv[])
{
    char* message = new char[1143];
    strcpy_s(message,1143, "Uid nx, aex jcdjipx iu wzux zp, ta wxtpa jtdaws, ai etkx vis.\
Dcos zyexdzaxr aex Jxdw jezwipijes iu etkzyg nidx aety iyx hts\
ai ri aex ptnx aezyg. Z zyexdzaxr aeta jezwipijes udin Wtdds Htww,\
hei zp ns exdi tqactwws. Z htya ai ntfx Dcos cpxdp udxx. Z htya ai\
gzkx aexn aex udxxrin ai qeiipx. Jxijwx tdx rzuuxdxya. Jxijwx qeiipx\
rzuuxdxya qdzaxdzt. Oca zu aexdx zp t oxaaxd hts tniyg ntys\
twaxdytazkxp, Z htya ai xyqicdtgx aeta hts os ntfzyg za qinuidatowx.\
Pi aeta\'p heta Z\'kx adzxr ai ri.\
Z htya ai piwkx jdiowxnp Z nxxa zy aex rtzws wzux os cpzyg qinjcaxdp,\
pi Z yxxr ai hdzax jdigdtnp. Os cpzyg Dcos, Z htya ai qiyqxyadtax aex\
aezygp Z ri, yia aex ntgzqtw dcwxp iu aex wtygctgx, wzfx patdazyg hzae\
jcowzq kizr  pinxaezyg pinxaezyg pinxaezyg ai pts, \"jdzya exwwi hidwr.\"\
Z vcpa htya ai pts, \"jdzya aezp!\" Z riy\'a htya tww aex pcddicyrzyg\
ntgzq fxshidrp. Z vcpa htya ai qiyqxyadtax iy aex atpf. Aeta\'p aex otpzq\
zrxt. Pi Z etkx adzxr ai ntfx Dcos qirx qiyqzpx tyr pcqqzyqa.\
Scfzezdi Ntapcniai. (hhh.tdaznt.qin/zyak/dcos)\0");
 
    /* in the main */
    const char* freqLang = "TEOIARNSHLMYUCWDGPFBVKJ";
 
    decryptMessage( message, freqLang );
 
    delete[] message;
    return 0;
}

#define TOTAL_LETTER 26


void decryptMessage( char* text, const char* );

int _tmain(int argc, _TCHAR* argv[])
{
    char* message = new char[1143];
    strcpy_s(message,1143, "Uid nx, aex jcdjipx iu wzux zp, ta wxtpa jtdaws, ai etkx vis.\
Dcos zyexdzaxr aex Jxdw jezwipijes iu etkzyg nidx aety iyx hts\
ai ri aex ptnx aezyg. Z zyexdzaxr aeta jezwipijes udin Wtdds Htww,\
hei zp ns exdi tqactwws. Z htya ai ntfx Dcos cpxdp udxx. Z htya ai\
gzkx aexn aex udxxrin ai qeiipx. Jxijwx tdx rzuuxdxya. Jxijwx qeiipx\
rzuuxdxya qdzaxdzt. Oca zu aexdx zp t oxaaxd hts tniyg ntys\
twaxdytazkxp, Z htya ai xyqicdtgx aeta hts os ntfzyg za qinuidatowx.\
Pi aeta\'p heta Z\'kx adzxr ai ri.\
Z htya ai piwkx jdiowxnp Z nxxa zy aex rtzws wzux os cpzyg qinjcaxdp,\
pi Z yxxr ai hdzax jdigdtnp. Os cpzyg Dcos, Z htya ai qiyqxyadtax aex\
aezygp Z ri, yia aex ntgzqtw dcwxp iu aex wtygctgx, wzfx patdazyg hzae\
jcowzq kizr  pinxaezyg pinxaezyg pinxaezyg ai pts, \"jdzya exwwi hidwr.\"\
Z vcpa htya ai pts, \"jdzya aezp!\" Z riy\'a htya tww aex pcddicyrzyg\
ntgzq fxshidrp. Z vcpa htya ai qiyqxyadtax iy aex atpf. Aeta\'p aex otpzq\
zrxt. Pi Z etkx adzxr ai ntfx Dcos qirx qiyqzpx tyr pcqqzyqa.\
Scfzezdi Ntapcniai. (hhh.tdaznt.qin/zyak/dcos)\0");

    /* in the main */
    const char* freqLang = "TEOIARNSHLMYUCWDGPFBVKJ";

    decryptMessage( message, freqLang );

    delete[] message;
    return 0;
}

To copy to clipboard, switch view to plain text mode 

Regards

[wysota]

What if you use "message" instead of "ptr"? What's the use of ptr anyway if it points to the same thing as message and both those pointers are const? Also check that line #60 of your snippet is correct.

[franco.amato]

What if you use "message" instead of "ptr"? Also check that line #60 of your snippet is correct.

Hi wysota initially I got the error using message. So I did the test copyng the pointer to ptr just for test getting exactly the same error.
My app crash at line 52.
while( (c = ptr[index]) != '\0' ) // changing to while( (c = message[index]) != '\0' ) I get the same problem

Debugging I get the message 'invalid pointer' ???? I'm becoming crazy

[wysota]

Check if "index" is within a valid range!

[franco.amato]

Check if "index" is within a valid range!

I correct the last loop:

while( (c = message[k]) != '\0' )
    {
        if (isalpha(c))
        {    
            c = toupper(c);
            pdest = strchr(freqLangCrypt, c);
            if( pdest != NULL )
            {
                int index = (int)(pdest - freqLangCrypt);
                putchar(freqLang[index]);
            }
            else
                putchar(c);
        }//if(isalpha(c))
        else
            putchar(c);
        k++;
    }//while

while( (c = message[k]) != '\0' )
    {
        if (isalpha(c))
        {    
            c = toupper(c);
            pdest = strchr(freqLangCrypt, c);
            if( pdest != NULL )
            {
                int index = (int)(pdest - freqLangCrypt);
                putchar(freqLang[index]);
            }
            else
                putchar(c);
        }//if(isalpha(c))
        else
            putchar(c);
        k++;
    }//while

To copy to clipboard, switch view to plain text mode 

Now it get the right index into the frecuency vector but.
Thanx