Segmentation Fault in function pointer [closed] - c

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I have an example code as below, because I'm not familiar with the function pointer so that I cannot find out what is happening at
ret = (p_local->str)(10,b_in); (segmentation fault)
#include "stdio.h"
typedef int (*check)(const int a, char * const b[]);
typedef struct ST_T_COMMAND
{
char *chuoi;
check str;
} T_COMMAND;
const T_COMMAND *p_global;
int main()
{
int ret;
const T_COMMAND *p_local;
char *b_in[] = {"1234", "abchd"};
T_COMMAND str_new;
p_global = &str_new;
str_new.chuoi = "1234";
p_local = p_global;
if(strcmp(p_local->chuoi, b_in[0]) == 0)
{
ret = (p_local->str)(10, b_in);
printf("ret = %d\n", ret);
}
else
{
printf("else\n");
}
return 0;
}
I want to pass that segmentation fault. And please tell me what is wrong with my code

Answer 1

Here
typedef int (*check)(const int a, char * const b[]);
you have declared the function pointer i.e check is the function pointer name, it can points to any function whose input argument are int and char* const [] type & which returns int type.
And here
ret = (p_local->str)(10, b_in); /* calling via function pointer */
you are trying to call via function pointer but you haven't initialized function pointer anywhere. You need to initialize function pointer first before calling it.
Also
const T_COMMAND *p_local; /* initialize it here itself */
above syntax means where p_local points that is constant i.e when you will do like
p_local->str = funHandler;
as I did below, compiler will not allow it to modify.
Same with p_global, if you make this as const earlier, you can't do like
const T_COMMAND *p_global;
p_local = p_global; /* not possible due to above const declaration of p_global */
Try this version:
#include <stdio.h>
#include <string.h>
typedef int (*check)(const int a, char * const b[]);
typedef struct ST_T_COMMAND
{
char *chuoi;
check str;
}T_COMMAND;
T_COMMAND *p_global; /* removed const */
int funHandler(int num, char* const buf[10])
{
printf("in funHandler() %d %s\n", num, buf[0]);
return num;
}
int main(void)
{
int ret;
T_COMMAND *p_local; /* removed const */
char * b_in[] = {"1234","abchd"};
T_COMMAND str_new;
p_global = &str_new;
str_new.chuoi = "1234";
p_local = p_global;
if(strcmp(p_local->chuoi,b_in[0]) == 0)
{
p_local->str = funHandler; /* initialize function pointer, you missed this */
ret = (p_local->str)(10,b_in);
printf("ret = %d\n",ret);
}
else
{
printf("else\n");
}
return 0;
}

Answer 2

ret = (p_local->str)(10,b_in);
You are calling the function p_local->str without initializing it first.
You need to set a value to plocal->str (or any of the equivalent values in your program i.e. p_global, str_new)
This value should be a function that you have defined elsewhere which matches the type of the function pointer i.e. parameters of const int a and char * const b[]