Access violation on copying array contents.

[dbuser]

Dear experts:
Hope you can point my error here. This function of mine receives an
array of length 32 and then the for loop adds some scrambled characters
at patterns. I think, I can not read the array w[] beyond 32 , but dont
know how to achieve the result. Thanks a lot for help !

void scramble( char *w, int key)
{
x = key; // key = (0-9)
int len = strlen(w);
cout << "length is:" << len << endl; // 32
len = (len + len/x); // 48
cout << "length is:" << len << endl;
char s[] = "@#$"; //array to hold scramble characters
int n = strlen(s);
int i,j,k,m=0;
char * c;
c = new char[len+1];
memset(c, 0, sizeof(c));
//if (c == NULL) exit(1);
for (i=0,j=0,k=0; i<len-1; i++){
if(k<x) {
c[j++] = w;k++;
}
else {
if(m<n)
c[j++] = s[m++];
else {
c[j++] = s[0]; m = 1;}
c[j++]=w; k=1; }
}
cout << "scrambled output is :" << c << endl;
delete c;
}

The output is this, which is desired but it has run time error as
mentioned.
input is : ba ced fhgi kzl nmpo qsr tvuxwzy
scrambled output is :ba@ c#ed$ f@hg#i $kz@l #nm$po@ q#sr$ t@vu#xw$zy@

 

[Victor Bazarov]

Hope you can point my error here. This function of mine receives an
array of length 32 and then the for loop adds some scrambled characters
at patterns. I think, I can not read the array w[] beyond 32 , but dont
know how to achieve the result. Thanks a lot for help !

void scramble( char *w, int key)

If 'w' is the array the bounds of which you're not supposed to cross,
then this function needs to know the bounds -- pass the actual size of
that array into the function, as another argument.

{
x = key; // key = (0-9)

Where is 'x' declared? Is it a global variable?

int len = strlen(w);
cout << "length is:" << len << endl; // 32

Is '32' what it prints out?

len = (len + len/x); // 48

What does '48' mean? x == 2? What is 'len' now?

cout << "length is:" << len << endl;

Does it print 48 here?

char s[] = "@#$"; //array to hold scramble characters

Four letters is the size of your 's' array.

int n = strlen(s);

n is 3.

int i,j,k,m=0;
char * c;

Why not merge the two statements into one?

c = new char[len+1];
memset(c, 0, sizeof(c));

sizeof(c) is 4. You really need to do 'memset(c, 0, len+1)' here.

//if (c == NULL) exit(1);

^^^^^^^^^^^^^^^^^^^^^^^^^
Get rid of this comment, it has no value.

for (i=0,j=0,k=0; i<len-1; i++){
if(k<x) {
c[j++] = w;k++;

So, you copy the characters if 'k' is smaller than the 'key'. IOW, you
leave up to 'key' characters unchanged.

}
else {
Otherwise...

if(m<n)
c[j++] = s[m++];

You insert a scrambled character until they are all used up (m>=n)

else {
c[j++] = s[0]; m = 1;}

Otherwise you start over...

c[j++]=w; k=1; }

... and still append the source character...

}
cout << "scrambled output is :" << c << endl;
delete c;

delete[] c;

}

The output is this, which is desired but it has run time error as
mentioned.
input is : ba ced fhgi kzl nmpo qsr tvuxwzy
scrambled output is :ba@ c#ed$ f@hg#i $kz@l #nm$po@ q#sr$ t@vu#xw$zy@

Well, your calculation of 'len' may be a bit flawed. Try adding 1 to it.

V

 

[Dan Cernat]

Dear experts:
Hope you can point my error here. This function of mine receives an
array of length 32 and then the for loop adds some scrambled characters
at patterns. I think, I can not read the array w[] beyond 32 , but dont
know how to achieve the result. Thanks a lot for help !

void scramble( char *w, int key)
{
x = key; // key = (0-9)
int len = strlen(w);
cout << "length is:" << len << endl; // 32
len = (len + len/x); // 48

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ replace with
int newLen = (len + len/x);

cout << "length is:" << len << endl;
char s[] = "@#$"; //array to hold scramble characters
int n = strlen(s);
int i,j,k,m=0;
char * c;
c = new char[len+1];

^^^^^^^^^^^^^^^^^^^ c = new char[newLen + 1];

memset(c, 0, sizeof(c));

^^^^^^^ sizeof(c) is 4 on 32 bit machines
memset(c, 0, newLen + 1);

//if (c == NULL) exit(1);
for (i=0,j=0,k=0; i<len-1; i++){
if(k<x) {
c[j++] = w;k++;
}
else {
if(m<n)
c[j++] = s[m++];
else {
c[j++] = s[0]; m = 1;}
c[j++]=w; k=1; }
}
cout << "scrambled output is :" << c << endl;
delete c;

^^^^^^^^^^^^^^^^^^^^
delete[] c;

}

The output is this, which is desired but it has run time error as
mentioned.
input is : ba ced fhgi kzl nmpo qsr tvuxwzy
scrambled output is :ba@ c#ed$ f@hg#i $kz@l #nm$po@ q#sr$ t@vu#xw$zy@

work on the indentation style. also, write one statement per line.

your for loop was running 48 times, and J was incremented 2 some times
(that is how it works) so you were writing past the end of newly
allocated memory for c

/dan

 

[dbuser]

Thanks a lot for your valuable suggestions. I corrected mistakes but to
fix run time error, I had to read source array upto its own length like
this:
for (i=0,j=0,k=0,p=0; i<newLen,p<len; i++,p++){
if(k<x) {
c[j++] = w[p];k++;
}
else {
if(m<n)
c[j++] = s[m++];
else {
c[j++] = s[0];
m = 1;
}
c[j++]=w[p];
k=1;
}
}

 

[Thomas J. Gritzan]

Thanks a lot for your valuable suggestions. I corrected mistakes but to
fix run time error, I had to read source array upto its own length like
this:
for (i=0,j=0,k=0,p=0; i<newLen,p<len; i++,p++){

^^^^^^^^^^^^^^
Do you mean (i<newLen && p<len) or (i<newLen || p<len)?
The comma operator throws away the result of the first part.

if(k<x) {
c[j++] = w[p];k++;
}
else {
if(m<n)
c[j++] = s[m++];
else {
c[j++] = s[0];
m = 1;
}
c[j++]=w[p];
k=1;
}
}

Th.