c - dynamic strings in struct -

i having problem understanding concept of dynamic memory allocation, have code encountering segfault perhaps 1 may have insight?

 #include <stdio.h>  #include <stdlib.h>   typedef struct tname {    char **stringa;    int capacity; } tname;  tname *createtname(int length); tname *destroytname(tname *l);  int main(void) {     tname *ll = createtname(10); }  tname *createtname(int length) {     tname *temp;     int i;     temp->capacity = length;      temp->stringa= (char**) malloc(sizeof(char*) * length);     for(i=0;i<length;i++)        temp->stringa[i] = (char*) malloc(sizeof(char)*50);      return temp; } 

when call run program segfault, can assist me please?

your problem here:

temp->capacity = length; 

you asigning value variable, doesn't have memory yet. have allocate memory struct to.

use this:

tname *temp = malloc( sizeof(tname) ); 

if write tname *temp, compiler allocate 4 bytes (or 8 in 64bit systems) pointer. wont't allocate momory, pointer pointing to.

another problem @ malloc, allocates memory string - should this:

temp->stringa = malloc(length+1); 

fist of all, don't have multiply sizeof(char*) (which again 4 or 8 bytes), sizeof(char). variabletype char needs 1 byte, don't have mulitply @ all.

but must not forget allocate 1 extra-byte string, if want use string-operations. byte needed stroe ascii-0, specifies end of string.

if forget byte, program can result in strange output, , in sefgaults.

and loop:

for(i=0;i<length;i++)        temp->stringa[i] = (char*) malloc(sizeof(char)*50); 

i don't know want achieve it, can add more information?