History in own C Shell - c

Question

I'm writing my own C Shell and I'm having trouble implementing something to maintain a history of commands.
I'd like to store it in a struct with an integer and string (so I can keep the command and its place in memory together), and I only want to store 20 elements.
I've tried using code from questions other people have asked on this website but when I compile it, it just returns a segmentation fault, so I'm guessing there's something wrong with the pointers.
Here's all the code I found relating to the history:
char** cmdHistory; /* command history - no longer than 20 elements & null terminated */
int historySize = 0;
void addToHistory(char* newEntry) {
char** h;
int historySize = 0;
while (*cmdHistory != NULL)
if (sizeof(cmdHistory) == 20) {
char** newPtr = ++cmdHistory;
free(cmdHistory[0]);
cmdHistory = newPtr;
h = (char**)realloc(cmdHistory,20*sizeof(int));
cmdHistory = h;
cmdHistory[20] = newEntry;
} else {
h = (char**)realloc(cmdHistory,sizeof(int)+sizeof(cmdHistory));
cmdHistory = h;
cmdHistory[historySize] = newEntry;
++historySize;
}
}
void printHistory() {
char** currCmd = cmdHistory;
printf("\n\n");
while (*currCmd != NULL) {
printf("%s\n", *currCmd);
currCmd++;
}
printf("\n\n");
}
int main() {
cmdHistory[20] = NULL; /* null terminate the history */
}
I'm pretty useless with C, so any help is much appreciated.

Answer 1

You can use link list to implement history, always adding present command at the head. Like this:
#include <stdio.h>
typedef struct history
{
char *ent;
struct history * next;
}hist;
hist *top = NULL;
void add(char *s)
{
hist *h = (hist *) malloc(sizeof(hist));
h->ent = s;
h->next = top;
top = h;
}
void print()
{
hist *i;
for (i = top; i != NULL; i = i->next)
printf("%s\n", i->ent);
}
int main()
{
add("command");
print();
}