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Changing a static array to a dynamic one with minimal changes?

I have C code that creates an array of char pointers like this:

char* arr[100];

I am using each element in this array to point to some string that is calculated by another function. So basically arr [0] points to line1 and arr [1] to line2 and so on.

This works great. However, I am now asked to be more flexible by specifying the number of lines as a parameter.

How can I do this with minimal changes to my code? I understand that I need to use malloc. However, I am getting a lot of warnings in all the assignment statements I have had before. I changed the array declaration as follows:

char* arr = (char*)malloc(n * sizeof(char*)); //where n is provided by user

I thought I only needed to change the ad. Now all assignment instructions give warnings ("assignment makes an integer from a pointer without a cast"). Below is an example of an assignment statement:

arr[i] = str; //where str is defined as char* and is calculated by another function

Am I missing something?

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4 answers


If you want to create an array char *

you will need char **arr

. Think of it as an array char *

- if you have an array int

, you will int *

. Since you have an array char *s

, you need char **

.



char** arr = malloc(n * sizeof(char*));
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You declare arr

as a pointer to char

: either a single string, or an array char

s if you prefer.

To allocate an array of pointers, declare arr

as



char **arr = malloc(n * sizeof(char *));

By the way, remove the cast: unnecessary in C. See also Question 7.7 in the comp.lang.c FAQ .

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you want to declare arr

as char **

as you are pointing to an array of pointers. If you arr

only declare as char *

(not char **

or char *[]

), you only have one line.

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Don't forget that the string is also an array ( char *

), so you need an array of pointers, which should look like this:

char** arr = (char**)malloc(n * sizeof(char*));
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