When to use malloc for char pointers

Question

I m specifically focused on when to use malloc on char pointers  char  ptr  ptr    something      code       code    ptr    something else     Would a malloc be in order for something as trivial as this  If yes  why  If not  then when is it necessary for char pointers

User · Answer

malloc is for allocating memory on the free-store  If you have a string literal that you do not want to modify the following is ok   char  literal    foo     However  if you want to be able to modify it  use it as a buffer to hold a line of input and so on  use malloc   char  buf    char   malloc BUFSIZE      define BUFSIZE before           free buf

User · Answer

malloc for single chars or integers and calloc for dynamic arrays  ie pointer     int   malloc sizeof int      NULL   you can do arithmetic within the brackets of malloc but you shouldnt because you should use calloc which has the definition of void calloc count  size which means how many items you want to store ie count and size of data ie int   char etc

User · Answer

Everytime the size of the string is undetermined at compile time you have to allocate memory with malloc  or some equiviallent method   In your case you know the size of your strings at compile time  sizeof  something   and sizeof  something else

User · Answer

Use malloc   when you don t know the amount of memory needed during compile time  In case if you have read-only strings then you can use const char  str    something     Note that the string is most probably be stored in a read-only memory location and you ll not be able to modify it  On the other hand if you know the string during compiler time then you can do something like  char str 10   strcpy str   Something    Here the memory is allocated from stack and you will be able to modify the str  Third case is allocating using malloc  Lets say you don r know the length of the string during compile time  Then you can do char  str   malloc requiredMem   strcpy str   Something    free str

User · Answer

As was indicated by others  you don t need to use malloc just to do   const char  foo    bar     The reason for that is exactly that  foo is a pointer  mdash  when you initialize foo you re not creating a copy of the string  just a pointer to where  bar  lives in the data section of your executable   You can copy that pointer as often as you d like  but remember  they re always pointing back to the same single instance of that string   So when should you use malloc   Normally you use strdup   to copy a string  which handles the malloc in the background   e g   const char  foo    bar   char  bar   strdup foo      now contains a new copy of  bar     printf   s n   bar          prints  bar     free bar                    frees memory created by strdup      Now  we finally get around to a case where you may want to malloc if you re using sprintf   or  more safely snprintf   which creates   formats a new string   char  foo   malloc sizeof char    1024             buffer for 1024 chars    snprintf foo  1024    s -  s n    foo    bar       puts  foo - bar n  in foo    printf foo                                         prints  foo - bar     free foo                                           frees mem from malloc

[c] When to use malloc for char pointers

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