invalid pointer: 0x08ce6158 ***

[Sebouh]

I'm very close of shooting myself in the head right now. Why in hell does free(xx[0]) give me an error: *** glibc detected *** free(): invalid pointer: 0x08ce6158 ***

// The function returns something like the argv[] parameter in main.
char** parser (char* ch)
{
    char** xx = NULL;
    char* temp;            // contains the input which will be modified when using strtok
    int length = strlen (ch);    // length of the string
    char* token;
    int numOfTokens = 0;
    int i = 0;
 
        // copy to use it for counting tokens, since it gets modified (can't use ch)
    temp = (char*)malloc (length + 1);
    strcpy (temp, ch);        
 
    token = strtok(temp, " ");
    while (token != NULL)
    {    numOfTokens++;    token = strtok(NULL, " ");    }
 
    xx = (char**)malloc (1 * numOfTokens + 1);
    for (i = 0; i < numOfTokens; i++)
        xx[i] = (char*)malloc (50);
 
    token = strtok(ch, " ");
    strcpy(xx[0],token);     // A living proof that show xx[0]is freeable
 
 
    i = 1;
    while ((token = strtok(NULL, " \n")) != NULL)
    {    
        strcpy (xx[i], token);
        i++;
    }
    xx[i] = NULL;     // Last arg is NULL
    free (token);
    free (xx[0]);      // my bane!!!!!
    free (temp);
    return xx;
}

Please anyone. This is driving me crazy!

Thank you!

[gpraghuram]

Hi,
The issue is the memory allocation
xx = (char**)malloc (1 * numOfTokens + 1);
change this to
xx = (char**)malloc (sizeof(char*) * numOfTokens + 1);


Thanks
Raghuram

[r035198x]

Changed thread title.

P.S Is the gun loaded?

[Sebouh]

I'm reloading the gun.


It didn't work. I didn't think it would have made any difference either. A pointer is always 1 byte long.

[gpraghuram]

Hi,
What is the input string you are passing as argument to this function.?
I tried with input "This is true" ad it is working fine.
Thanks
Raghuram

[Sebouh]

Hi,
What is the input string you are passing as argument to this function.?
I tried with input "This is true" ad it is working fine.
Thanks
Raghuram

I'm passing "/root/CMPS272_a2/test-batch 2 3".
It's supposed to be an arguement ofr execvp().

[gpraghuram]

Hi,
I have made some minor modifications in the code and it is working fine for me.
Initially i also got the sebmentaion fault..

char** parser (char* ch)
{
    char** xx = NULL;
    char* temp;            // contains the input which will be modified when using strtok
    char* token;
    int numOfTokens = 0;
    int i = 0;
    int length = strlen (ch);    // length of the string
 
        // copy to use it for counting tokens, since it gets modified (can't use ch)
    temp = (char*)malloc (length + 1);
    strcpy (temp, ch);        
 
    token = strtok(temp, " ");
    while (token != NULL)
    {    
        numOfTokens++;    
        token = strtok(NULL, " ");    
    }
 
    //xx = (char**)malloc (1 * numOfTokens + 1);
    xx = (char**)malloc (sizeof(char*) * numOfTokens + 1);
    for (i = 0; i <= numOfTokens; i++)
        xx[i] = (char*)malloc (50);
 
    strcpy (temp, ch);
    //token = strtok(ch, " ");
    token = strtok(temp, " ");
    strcpy(xx[1],token);     // A living proof that show xx[0]is freeable
    i = 2;
    while ((token = strtok(NULL, " ")) != NULL)
    {    
        strcpy (xx[i], token);
        i++;
    }
    xx[i] = NULL;     // Last arg is NULL
    free (token);
    free (xx[0]);      // my bane!!!!!
    free (temp);
    return xx;
}
 

Thanks
Raghuram

[Sebouh]

Hi,
I have made some minor modifications in the code and it is working fine for me.
Initially i also got the sebmentaion fault..

char** parser (char* ch)
{
    char** xx = NULL;
    char* temp;            // contains the input which will be modified when using strtok
    char* token;
    int numOfTokens = 0;
    int i = 0;
    int length = strlen (ch);    // length of the string
 
        // copy to use it for counting tokens, since it gets modified (can't use ch)
    temp = (char*)malloc (length + 1);
    strcpy (temp, ch);        
 
    token = strtok(temp, " ");
    while (token != NULL)
    {    
        numOfTokens++;    
        token = strtok(NULL, " ");    
    }
 
    //xx = (char**)malloc (1 * numOfTokens + 1);
    xx = (char**)malloc (sizeof(char*) * numOfTokens + 1);
    for (i = 0; i <= numOfTokens; i++)
        xx[i] = (char*)malloc (50);
 
    strcpy (temp, ch);
    //token = strtok(ch, " ");
    token = strtok(temp, " ");
    strcpy(xx[1],token);     // A living proof that show xx[0]is freeable
    i = 2;
    while ((token = strtok(NULL, " ")) != NULL)
    {    
        strcpy (xx[i], token);
        i++;
    }
    xx[i] = NULL;     // Last arg is NULL
    free (token);
    free (xx[0]);      // my bane!!!!!
    free (temp);
    return xx;
}
 

Thanks
Raghuram

Thanks for the effort mate, but i can't see which change solved the real problem. i think if you change the free(xx[0]) to free(xx[1]), you'll ge the same problem, thought i'm not sure since my program requires xx[0] to have the prog name, just like argv[].

[Banfa]

It didn't work. I didn't think it would have made any difference either. A pointer is always 1 byte long.

This is quite seriously wrong. If a pointer was only 1 byte long then it would only be able to address 256 bytes of memory (at addresses 0 to 255).

On many systems a pointer is the same size as an int, but that is a rule of thumb rather than a specification. Pointers are no specific size except to say that they are generally large enough to access the entire memory range for the target system. Additionally pointers to different types do not have to be the same size or have the same bit pattern.

I do not know if this is the cause of you problem but there is still an error in

xx = (char**)malloc (sizeof(char*) * numOfTokens + 1);
 

Operator precedence is causing this to allocated sizeof(char *) -1 bytes too few so you are writing off the the end of the allocated memory and invoking undefined behaviour.

You need parentheses round the addition

xx = (char**)malloc (sizeof(char*) * (numOfTokens + 1));
 

[Sebouh]

This is quite seriously wrong. If a pointer was only 1 byte long then it would only be able to address 256 bytes of memory (at addresses 0 to 255).

On many systems a pointer is the same size as an int, but that is a rule of thumb rather than a specification. Pointers are no specific size except to say that they are generally large enough to access the entire memory range for the target system. Additionally pointers to different types do not have to be the same size or have the same bit pattern.

I do not know if this is the cause of you problem but there is still an error in

xx = (char**)malloc (sizeof(char*) * numOfTokens + 1);
 

Operator precedence is causing this to allocated sizeof(char *) -1 bytes too few so you are writing off the the end of the allocated memory and invoking undefined behaviour.

You need parentheses round the addition

xx = (char**)malloc (sizeof(char*) * (numOfTokens + 1));
 

Damn it!
You're totally right Banfa. I have no idea why i though a pointer is 1 byte long. I guess it slipped my mind. I guess that's why i didn't see the precedence thing either.
Thanks alot!