Dynamically create an array of strings with malloc

Question

I am trying to create an array of strings in C using malloc  The number of strings that the array will hold can change at run time  but the length of the strings will always be consistent   I ve attempted this  see below   but am having trouble  any tips in the right direction will be much appreciated    define ID LEN 5 char  orderedIds  int i  int variableNumberOfElements   5     Hard coded here     orderedIds   malloc variableNumberOfElements    ID LEN   1      Ultimately I want to be able to use the array to do this   strcpy orderedIds 0   string1   strcpy orderedIds 1   string2      etc

User · Answer

Given that your strings are all fixed-length (presumably at compile-time?), you can do the following:

char (*orderedIds)[ID_LEN+1]
    = malloc(variableNumberOfElements * sizeof(*orderedIds));

// Clear-up
free(orderedIds);

A more cumbersome, but more general, solution, is to assign an array of pointers, and psuedo-initialising them to point at elements of a raw backing array:

char *raw = malloc(variableNumberOfElements * (ID_LEN + 1));
char **orderedIds = malloc(sizeof(*orderedIds) * variableNumberOfElements);

// Set each pointer to the start of its corresponding section of the raw buffer.
for (i = 0; i < variableNumberOfElements; i++)
{
    orderedIds[i] = &raw[i * (ID_LEN+1)];
}

...

// Clear-up pointer array
free(orderedIds);
// Clear-up raw array
free(raw);

User · Answer

define ID LEN 5 char   orderedIds  int i  int variableNumberOfElements   5     Hard coded here     orderedIds    char    malloc variableNumberOfElements    ID LEN   1    sizeof char

User · Answer

You should assign an array of char pointers  and then  for each pointer assign enough memory for the string   char   orderedIds   orderedIds   malloc variableNumberOfElements   sizeof char     for  int i   0  i  lt  variableNumberOfElements  i        orderedIds i    malloc  ID LEN 1    sizeof char       yeah  I know sizeof char  is 1  but to make it clear      Seems like a good way to me  Although you perform many mallocs  you clearly assign memory for a specific string  and you can free one block of memory without freeing the whole  string array

User · Answer

char   orderIds   orderIds   malloc variableNumberOfElements   sizeof char      for int i   0  i  lt  variableNumberOfElements  i        orderIds i    malloc  ID LEN   1    sizeof char      strcpy orderIds i   your string i

[c] Dynamically create an array of strings with malloc

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