Thread: string and pointer

Depends how string is declared and what 'pointer' is.

If it's a 2d array of characters, and pointer is a pointer to a character then yes.

Why not compile and see for yourself!?

the program compile and run but got error message. Can anyone help me?

Code:

#include <stdio.h>
#include <math.h>
#include <string.h>
#include <ctype.h>

#define HISTORY_SIZE 10
#define MAX_STRING_LEN 100
#define  MAX_CMD_LEN 10

void printHistory( char history[][MAX_CMD_LEN], int size);
int processCommand( char *current, char *cmd, char *result); 
void updateHistory( char history[][MAX_CMD_LEN], const char *cmd, int size);

int main(void)
{
	int i;
	char cmd[MAX_CMD_LEN]="";
	char current[MAX_STRING_LEN]="";
	char result[MAX_STRING_LEN]="";
	char history_table[HISTORY_SIZE][MAX_CMD_LEN];
	
	int history_size = 0;
	int flag;

	printf("Enter command [help] for a list of commands\n");

	do {
		
		printf("cmd> ");
		gets(cmd); //get a command from user.

                        if(strcmp( cmd, "hist") == 0) {
			printHistory( history_table, history_size);
		}
		else {
			flag= processCommand(current, cmd, result);
		}
                        if( cmd !=""){
			updateHistory(history_table, cmd, history_size);
			history_size++;
		}
	}while (flag!=1);
	return 0;
}

void updateHistory( char history[][10], const char *cmd, int size)
{
	
	if(cmd != '\0'){
		history[size][0]=*cmd;
		size=size+1;
	}
	
}

From your code it's evident you really have no idea what's going on.

I suggest you start with the basics first, er yes... even more basic than that.
Start by following the tutorials on this site, mainly the arrays & pointer sections.

And also read FAQ
for example Why gets() is bad / Buffer Overflows

for print the array of strings. I can use this code right?

Code:

for (i=0; i<=size; i++)
        puts (historytable[i]);

and for copying *cmd to historytable[][10]
i can use this code right?

Code:

for(i=0;i<=size;i++)
        historytable[size][0]=*cmd;

Yes, except you want i < size Remember, arrays are 0 based not 1 based.

ie, 5 1-based is
1, 2, 3, 4, 5

0 based
0, 1, 2, 3, 4

'size' specifies how many elements, not the end point.

Originally Posted by zacs7

Yes, except you want i < size Remember, arrays are 0 based not 1 based.

ie, 5 1-based is
1, 2, 3, 4, 5

0 based
0, 1, 2, 3, 4

'size' specifies how many elements, not the end point.

you are right.

and back to the main code above

Code:

size++

in the updatehistory function, it doesn't add one to the variable history_size. why is that?

Originally Posted by nenpa8lo

This copies first char of 'cmd' to first position of each string in historytable (which is wrong):

Code:

historytable[i][0]=*cmd;

you have to do it like this:

Code:

for (i = 0; i < size; i++)
    historytable[0][i] = *cmd++;  /* copy one character from 'cmd' shift pointer etc. */

this copies "whole" cmd into historytable[0], however you have to be aware to control where 'cmd' points - if 'cmd' and historytable[][] are the same size the you are safe.... hypothetically :-)

i would do like this:
[CODE]

Code:

for (i = 0; i <strlen(cmd); i++)
    historytable[size][i] = *cmd++;

i need to copy 9 more strings

this way nul-char is not copied and there are possibilities of memory overrun

there is function strcpy - used for copying C-strings

and better check that strlen(cmd) < 10 before copying...

of cource cmd buffer should be allocated somewhere... and fgets will prevent the memory overrun...

Do not edit your old posts - post new code version in the new post

See comments

Code:

int main(void)
{
	int i;
	char cmd[MAX_CMD_LEN]="";
	char current[MAX_STRING_LEN]="";
	char result[MAX_STRING_LEN]="";
	char history_table[HISTORY_SIZE][MAX_CMD_LEN];
	
	int history_size = 0;
	int flag; /* not initialized */
	
	printf("Enter command [help] for a list of commands\n");
	
	do {
		
		printf("cmd> "); /* add fflush(stdout); after this line */
		gets(cmd); /* possible memory overrun */
		
		if(strcmp( cmd, "hist") == 0) {
			printHistory( history_table, history_size); /* no prototype */
		}
		else {
			flag= processCommand(current, cmd, result); /* no prototype */
		}
		if( cmd !="") /* incorrect operation - use strcmp */
		{
			updateHistory(history_table, cmd, history_size); /* no prototype */			history_size++;
		}
	}while (flag!=1); /* used not initialized var if command was hist */
	return 0;
}

void updateHistory( char history[][10], const char *cmd, int size)
{
	
	if(cmd != '\0'){
		history[size][0]=*cmd; /* wrong - use strcpy */
		size=size+1; /* has no effect */
	}
	
}