void TestMultiDim()
{
char** mArray;
int rows = 50;
char* p;
char* q;
char* data = "John Doe";
size_t len;
len = rows * sizeof(char*);
mArray = (char **)malloc(len);
if(mArray == NULL)
{
exit(EXIT_FAILURE);
}
memset(mArray, 0, rows);
//Create the sub arrays
for(p = mArray; *p!='\0'; p++)
{
*p = malloc(len);
if(*p == NULL)
{
exit(EXIT_FAILURE);
}
memset(*p, 1, len);
}
//Populate Data
for(p = mArray; *p !='\0'; p++)
{
*p = data;
}
//Print out List
for(p = mArray; *p !='\0'; p++)
{
printf("%s\n", *p);
}
}
Memset and Multidimensional pointers
Author
Hi,
I'm trying to learn to properly use multidimension pointers. For some reason it is not creating the sub arrays. Can somebody please help on this - Multidimensional Pointers problems?
Thanks,
Jr
For starters iterate through every position of your array like so:
You're also not populating your data correctly.
Note there is no need to repeatedly call memset. However if you find you actually need your allocation initialized call calloc instead.
[Edited by - fpsgamer on June 14, 2008 12:35:36 AM]
for(p = mArray; p!=(mArray+rows); ++p){ ....}You're also not populating your data correctly.
//Populate Datafor(p = mArray; p!=(mArray+rows); ++p){ *p = (char*)malloc(strlen(data)+1); assert(*p); strcpy(*p, data);}Note there is no need to repeatedly call memset. However if you find you actually need your allocation initialized call calloc instead.
[Edited by - fpsgamer on June 14, 2008 12:35:36 AM]
Author
Ok Guys, I've got it to work however, it is now failing on freeing up the resource that I created with malloc. The current problem now is how to I correctly free this without getting the heap corruption errors in Visual Studio?
void TestMultiDim()
{
char** mArray;
int rows = 50;
char* p;
char* q;
int i;
char* data = "John Doe";
size_t len;
len = rows * sizeof(char*);
mArray = (char **)malloc(len);
if(mArray == NULL)
{
exit(EXIT_FAILURE);
}
//Create the sub arrays
//for(p = mArray; *p!='\0'; p++)
for(i = 0; i < rows; i++)
{
//*p = (char*)malloc(len);
mArray = (char*)malloc(len);
//if(*p == NULL)
if(mArray == NULL)
{
exit(EXIT_FAILURE);
}
//memset(*p, 0, len);
}
//Populate Data
//for(p = mArray; *p !='\0'; p++)
for(i = 0; i < rows; i++)
{
mArray = data;
//*p = data;
}
//Print out List
//for(p = mArray; *p !='\0'; p++)
for(i = 0; i < rows; i++)
{
printf("%s\n", mArray);
}
//Clean Up:
for(i = 0; i < rows; i++)
{
free(mArray);
mArray = NULL;
}
free(mArray);
}
void TestMultiDim()
{
char** mArray;
int rows = 50;
char* p;
char* q;
int i;
char* data = "John Doe";
size_t len;
len = rows * sizeof(char*);
mArray = (char **)malloc(len);
if(mArray == NULL)
{
exit(EXIT_FAILURE);
}
//Create the sub arrays
//for(p = mArray; *p!='\0'; p++)
for(i = 0; i < rows; i++)
{
//*p = (char*)malloc(len);
mArray = (char*)malloc(len);
//if(*p == NULL)
if(mArray == NULL)
{
exit(EXIT_FAILURE);
}
//memset(*p, 0, len);
}
//Populate Data
//for(p = mArray; *p !='\0'; p++)
for(i = 0; i < rows; i++)
{
mArray = data;
//*p = data;
}
//Print out List
//for(p = mArray; *p !='\0'; p++)
for(i = 0; i < rows; i++)
{
printf("%s\n", mArray);
}
//Clean Up:
for(i = 0; i < rows; i++)
{
free(mArray);
mArray = NULL;
}
free(mArray);
}
The problem is you're attempting to delete a pointer that points to a string literal.
Also the condition you're using to terminate iteration of your loop is undefined. Heap allocated buffers do not end with a NULL terminator.
You should re-read all the stuff I described in my earlier post.
Also the condition you're using to terminate iteration of your loop is undefined. Heap allocated buffers do not end with a NULL terminator.
You should re-read all the stuff I described in my earlier post.
Are you trying to allocate a list of strings?
But this is a bad way of having lists of strings anyway. Instead, use std::vector<std::string>
char** createStringArray (int count, const char* string){ char** strs = new char*[strings]; assert (strs); // allocate each string size_t len = strlen (string) + 1; for (int i = 0; i < strings; i++) { strs = new char[len]; assert (strs); strcpy (strs, string); } return strs;}void deleteStringArray (char** strings, int count){ for (int i = 0; i < count; i++) { // delete the strings delete [] strings; } // delete the string pointer array delete [] strings;}void setStringInArray (char** strings, int index, char* new_string){ // since this code bases buffer length on string length get both size_t idxlen = strlen (strings[index]); size_t newlen = strlen (new_string); // if not the same length reallocate to shorter or longer length if (newlen != idxlen) { delete [] strings[index]; strings[index] = new char[newlen+1]; } strcpy (strings[index], new_string);}But this is a bad way of having lists of strings anyway. Instead, use std::vector<std::string>
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