Array of char*

Django_Untaken

Hello all... how do I create array of char*. At the moment I have hardcoded the number of instances (large enough to hold tokens) but this should be generic. Example

int temp_array[2] = {0};
char* token1;
char* token2;

As you can see, I might not know how many tokens I need at run time. I want something like this

char* [] tokens;

How could I fix this? Thanks

Jochen Arndt

Create a variable for the array that is initially empty and a variable holding the size:

char **tokens = NULL;
unsigned tokenSize = 0;

Once you know the required number of items, allocate the array. How to do that depends if you are using C or C++:

tokenSize = items_to_store_in_array;

// C++
tokens = new char *[tokenSize];

/* C */
tokens = (char **)malloc(sizeof(char*) * tokenSize);

If you need to change the size use realloc with C. With C++ you should then avoid arrays and use a container like vector - C++ Reference[^] instead.

Django_Untaken

Jochen Arndt wrote:

How to do that depends if you are using C or C++:

Well I should have mentioned that earlier..... I am using C. Can you please edit your question (or append the code for C)

Jochen Arndt

The C code is there (the malloc call). Use something like this (for two tokens):

tokenSize = 2;
tokens = (char **)malloc(sizeof(char*) * tokenSize);
tokens[0] = token1;
tokens[1] = token2;

/* Use tokens array here */

/* Release memory and reset variables when not used anymore */
free(tokens);
tokens = NULL;
tokenSize = 0;

Huzifa Terkawi

std::vactor m_myArrayOfString ; m_myArrayOfString.push_back(new char[17]); ... ... in the end loop through vector and delete them one by one for(auto ptr : m_myArrayOfString) delete [] ptr ; m_myArrayOfString.clear();

huzifa

leon de boer

Only addition to Jochens answer is to remove confusion to you typedef the char* pointer

ptrCount = 2;
typedef char* CHARPTR;
CHARPTR* charPtrArray = (CHARPTR*)malloc(sizeof(CHARPTR)*ptrcount);

Now it looks like any other array The confusion exists because char** can be a couple of things in C you can't distinguish them without looking at the initialization code 1.) A pointer to a char* (always true) 2.) An array of char* (if initialized as such) 3.) A multidimensional char array (if initialized as such) Number 3 in particular usually causes mass confusion with students learning C. The typedef doesn't stop you assuming the wrong thing but it does give you language cues to what it is and is easier to read.

In vino veritas

Munchies_Matt

Think of an array of chars as a 2d map. So along the bottom the x axis can be considdered as an array of char pointers, each one pointing to a vertical array of chars going up in the y direction. So point 0,0 is a char** You can of course extend this to a 3 d map, with char*** Any point on the 2d map can be referenced by data[x][y] SO first you alloc how many you need in the x direction: char** data = alloc(xMax) Now each vertical collum can be alloced as data[0] = alloc(y1Max) data[1] = alloc(y2Max) And so on.