My char vector is saving the same value in every position - c

Question

Im trying to make a shell in linux. I need to save every command the user typed and when the user wants to see the history Ill show him the last 10 commands. Im using a char* historial[10]; but when the user type the second command it is saving in historial[0] and historial[1] the same thing. So if I type 10 different commands, it will save the last command 10 times. I dont know what Im doing wrong.
PS: my condition in the do while is not working neither.
int ejecutarCom(char* comando)
{ //executes the command
pid_t pid;
pid = fork();
int aux = 0;
if (pid < 0)
{
perror("Error");
return -1;
}
else if (pid == 0)
{
aux = execlp(comando, comando, NULL);
}
else
{
wait(NULL);
}
return aux;
}
char* historial[10]; //history vector
int cantidad = 0, tamano = 10; //quantity & size
void guardarEnHistorial(char* c)
{ //saves every command
if (cantidad < tamano)
{
historial[cantidad] = c;
}
if (cantidad == tamano)
{
cantidad = 0;
historial[cantidad] = c;
}
cantidad++;
}
void verHistorial()
{ //shows history
for (int i = 9; i >= 0; i--)
{
if (historial[0] == NULL)
break;
else if (historial[i] == NULL)
{
printf(" ");
}
else
printf("%i: %s\n", i, historial[i]);
}
}
int main()
{
char* comando = (char*) malloc(1024);
int x = 1;
do
{
printf("%s ", prompt);
fflush(stdout);
fgets(comando, sizeof(comando), stdin);
comando[strcspn(comando, "\n")] = '\0';
printf("%s\n", comando);
if (strcmp(comando, "hist") == 0)
{
verHistorial();
}
else
{
x = ejecutarCom(comando);
guardarEnHistorial(comando);
printf("%i\n", x);
}
} while (x != -1);

Answer 1

Modify your main function like below. Every location of your history array is pointing to same memory location hence you are getting the same information in every location. You have to allocate memory for each command like below:-
int main(){
char* comando=(char*) malloc(1024);
int x=1;
do{
printf("%s ",prompt);
fflush (stdout);
fgets(comando,sizeof(comando),stdin);
comando[strcspn(comando, "\n")] = '\0';
printf("%s\n",comando);
if(strcmp(comando,"hist")==0){
verHistorial();}
else{
x=ejecutarCom(comando);
guardarEnHistorial(comando);
comando=(char*) malloc(1024);// You need to allocate memory to store
//each history records. Also consider whether you really need 1024 bytes of memory make it small
printf("%i\n",x);
}}while(x!=-1);

Answer 2

You are storing a pointer to the command buffer, not the command itself. As the address of the command buffer doesn't change, but its contents does, every history entry will point to the same command buffer and thus will show the same command:
char* historial[10]; // history vector has only pointers
//...
historial[cantidad] = c; // stores a pointer
The following allocates and frees memory as appropriate:
void guardarEnHistorial(char* c)
{ //saves every command
if (cantidad == tamano) cantidad = 0;
if (historial[cantidad]) free(historial[cantidad]);
historial[cantidad]= malloc(strlen(c)+1);
strcpy(historial[cantidad], c);
cantidad++;
}

Answer 3

I dont know what Im doing wrong.
You are observing this behavior because the char pointers of historial array are pointing to same memory location comando. Check this statement of your program:
guardarEnHistorial(comando);
and in the guardarEnHistorial () function, you are doing:
historial[cantidad] = c;
Any changes you make to comando will reflect to all the members of historial array in which you have saved the command.
You can use strdup() to resolve this issue. Replace this:
guardarEnHistorial(comando);
with this:
guardarEnHistorial(strdup(comando));
^^^^
The strdup() function returns a pointer to a new string which is a duplicate of the string passed to it. strdup() allocates a memory for the new string using malloc and returns its pointer. Make sure to free it using free() once you are done with it. Like when inserting into historial array, you are rotating the insertion if the condition cantidad == tamano meets. Here, you need to free the element first and then insert the new element into the array otherwise there is a memory leaks in your program.