c - char *str[ ] pass by reference not working -

i passing char *str[] in function , adding contents in main function values unchanged.

from main calling lettercombinations function , calls function in editing valuees of char * str[] wwhihc changed there not reflected in letter combinations function

please me why not working

help(char *str[],char* curr,int index,char* digits,char** a,int *k)         {             if(strlen(curr)==strlen(digits))             {                 printf("%d",*k);                  str[*k]=(char*)malloc(strlen(digits)+1);                  str[*k]=curr;                 printf("%s %s %d\n",curr,str[*k],*k);                  *k=*k+1;                  return ;             }              int i;              char* loop=a[digits[index]-'0'];              int l=strlen(loop);             for(i=0;i<l;i++)             {                 curr[index]=loop[i];                  help(str,curr,index+1,digits,a,k);                 curr[index]='\0';             }         }   char** lettercombinations(char* digits, int* returnsize) {             char *str[100];               int i=0;             char* curr=malloc(sizeof(strlen(digits)+1));             char** a=(char**)malloc(10*sizeof(char*));           int siz=0;             a[0]="";             a[1]="";             a[2]="abc";             a[3]="def";             a[4]="ghi";             a[5]="jkl";             a[6]="mno";             a[7]="pqrs";             a[8]="tuv";             a[9]="wxyz";              help(str, curr, 0, digits,a,&siz);              printf("  %d",siz);             for(i=0;i<siz;i++)             {                 printf(" s   %s",str[i]);             }            // *returnsize=siz;             return str;             } 

if compile code should see warnings such as:

warning c4172: returning address of local variable or temporary warning c4100: 'returnsize' : unreferenced formal parameter 

returning address of local variable or temporary warning explains behaviour.

in code:

char** lettercombinations(char* digits, int* returnsize) {     char *str[100];    ...     return str; } 

you create array on stack, str. when return lettercombinations, variable goes out of scope , stack memory location gets cleaned up. ie memory address used str no longer valid.

you change caller passes in own char* variable fix issue. alternatively, malloc str , when return function, memory location still exists. caller have free memory location - messy.

after fixing ... move onto next bug.

the next thing notice in function have:

if (strlen(curr) == strlen(digits)) 

but curr not initialised. fix next. move onto next bug.

you should step through each line thinking through how variables populated in each line.