char *temp = ...;

// Copy to an existing STRING
STRING *str;
str_cpy(str, temp);

// Creating a new STRING:
STRING *str = str_create(temp);

// Setting a TEXT member
// If no string is set (should be default case), create one
if((input_txt.pstring)[0] == NULL)
    (input_txt.pstring)[0] = str_create(temp);
else
    str_cpy((input_txt.pstring)[0], temp);