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 · Accepted 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 < 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

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

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  lt  variableNumberOfElements  i          orderedIds i     amp raw i    ID LEN 1               Clear-up pointer array free orderedIds      Clear-up raw array free raw

[c] Dynamically create an array of strings with malloc

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