Initialisation and resize of array of character pointers - c

Question

If I create one array of character pointers of some size like:
char* temp[10];
//need intialisation here..
temp[0] = "BLAH";
temp[1] = "BLAH";
temp[3] = "BLAH";
.
.
.
temp[9] = "BLAH";
//Need reinitialise..
temp[10] = "BLAH";
temp[11] = "BLAH";
How do I initialise it?
How to re-initialise it with size 20 after some time?
Are malloc() and calloc() useful to do this? If yes then how to use with array of pointers to character?
[EDITED]
My code and requirement,
Basically i want read file in c but without wasting single character...
Here are the code to read data from text file,
FILE *ptr_file;
/* Allocate space for ten strings */
/* Allocate space for ten strings */
char** list = (char **)malloc(10 * sizeof(char));
/* Reallocate so there's now space for 20 strings */
/* And initialize the new entries */
ptr_file =fopen(LogFileCharName,"rb");
if (!ptr_file)
return 1;
int __index = 0;
wchar_t CurrentString[1000];
while(fgetws (CurrentString , 1000 , ptr_file) != NULL)
{
char* errorDes;
errorDes = new char[1000];
wcstombs(errorDes, CurrentString, 1000);
list[__index] = errorDes;
if( __index>10)
{
(char**)realloc(list, 20 * sizeof(char *));
}
__index++;
}
now when size exceeded 10 then in just need to resize that are.
for this i am using win32 console application type of microsoft visual studio.

Answer 1

You don't use arrays, but pointers and allocate on the heap, and then reallocate when needed:
/* Allocate space for ten strings */
char **temp = malloc(10 * sizeof(char *));
temp[0] = "Hello 1";
/* ... */
temp[9] = "Hello 10";
/* Reallocate so there's now space for 20 strings */
temp = realloc(temp, 20 * sizeof(char *));
/* And initialize the new entries */
temp[10] = "Hello 11";
As for initialization, it depends on what the contents of the strings are. Either you make it point to an already existing string (either string literals like in my example above, or other strings), or you allocate space for the strings on the heap as well.
Maybe something like this:
for (int i = 0; i < 10; i++)
{
char temp_string[10];
/* Create strings in the form "Hello 1" to "Hello 10" */
sprintf(temp_string, "Hello %d", i + 1);
/* Duplicate the temporary string */
temp[i] = strdup(temp_string);
}
Note: If you use e.g. strdup or malloc/calloc to allocate the actual strings, you of course have to free them as well.
After your updated question, I see a couple of problems with your code:
The first is that when do the check __index>10 then you're already two indexes out of bounds for the array. The check should be __index==9.
Doing the change above will also solve your other problem, that you will continuously reallocate once the index goes to 11 or higher.
Since you use new for the actual strings in the array, you have to use delete when freeing the actual strings.
Since you use new, you are using C++, for which there are much better facilities to handle things like this:
// Declare and open file
wifstream ifs(LogFileCharName);
std::vector<std::string> list;
std::wstring CurrentString;
while (std::getline(ifs, CurrentString))
{
// Get the needed length of the destination string
size_t length = wcstombs(nullptr, CurrentString.c_str(), 0);
char* tmp = new char[length + 1];
// Do the actual conversion
wcstombs(tmp, CurrentString.c_str(), length + 1);
// Add to list
list.emplace_back(tmp);
delete [] tmp;
}