string and pointer

can I write like this?

Code:

string[1][0] = *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?

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 :-)

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 strlen() is called at every iteration. So:

Code:

size=strlen(cmd);
for(i = 0; i < size; i++)
    {...}

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...

First of all can you tell what are you going to do with this code? Secondly there is few mistakes:

Originally Posted by phoebus

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

Code:

int main(void)
{
          char historytable[10][10];
           int history_size = 0;
            printf("cmd> ");
	gets(cmd); //get a command from user.    where is declared 'cmd' ? 
	updateHistory(historytable, cmd, history_size);
            printHistory( historytable, history_size);
           return 0;
}
void printhistory( char hist[][10], int size)
{
	int i;
	printf("Size of history: %d\n", size);
	for( i=0; i<=size; i++)  size is 0 so why you want to print it in loop ? 
	{
		puts(hist[i]);
	}
	printf("\n");
}

void updateHistory( char history[][10], const char *cmd, int size)
{
	
	if(cmd != '\0'){
		history[size][0]=*cmd;
		size=size+1;    this makes no sense as 'size' is on the stack! If you want to make permanent changes to size you have to pass it like : updateHistory(...., &size); and then in function body cach it like updateHistory(...., int *size)
	}
	
}

okay I fix my main function. Take a look at it. Sorry for the indent.

Originally Posted by vart

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...

If I want to use the strcpy function I have initalize

Code:

char history_table[HISTORY_SIZE][MAX_CMD_LEN];

like

Code:

char string[10]="";

but I don't know how to initialize a array of strings.
can anyone help?

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 */
	}
	
}