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 string
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"