C / C++ / MFC

30-Apr-07 18:04

Hi all:

Say:

char *string = NULL, *buffer = NULL;
int string_len = 0;

fgets(buffer);
string_len = strlen(buffer);
buffer[string_len] = '\0';
string = malloc(string_len+1);
strncpy(string, buffer, string_len);

return string;

Is my codes correct?

Thank you

David Nash30-Apr-07 18:38

David Nash

30-Apr-07 18:38

Its been a while since if coded in C, but did you allocate memory for buffer?

You should free the memory allocated for string as well.

regards,
David
http://users.bigpond.net.au/programming

C_Zealot30-Apr-07 19:34

30-Apr-07 19:34

That is what confuses me, David.

This is what I thought:

I have to put the string I read into somewhere (e.g. into a buffer) before I can use strlen() to get the length of the string.

Is there another way to accomplish this task? E.g. how do I know the length of the string I read before I put it to a buffer?

Thanks

Eytukan30-Apr-07 19:25

Eytukan

30-Apr-07 19:25

But where do you allocate memory for *buffer?
What about this:

    char* buffer = new char[10];
gets(buffer);
char* st=buffer;
printf("%s %s",st,buffer);
delete buffer;

Press: 1500 to 2,200 messages in just 6 days? How's that possible sir?
Dr.Brad :Well,I just replied to everything Graus did and then argued with Negus for a bit.

C_Zealot30-Apr-07 19:37

30-Apr-07 19:37

Hi VuNic:

Thank you for your reply.

I am still wondering if there is a way for me somehow get the length of the word I will read without declaring a pointer (buffer) which points to a char array of certain length?

Thank you

Eytukan30-Apr-07 20:37

Eytukan

30-Apr-07 20:37

Are you supposed to stick to "C" ? or you have the option of using std::string s?
why not use them? or you need to go for linked lists. like :

typedef struct stringz
	{
		char c;
		struct stringz* next;
	}st;
	st* str =(st*)malloc(sizeof(stringz));
	st* head = str;
	char c;
	while(c=getch())
	{
		if(c==13)
			break;
		str->c=c;
		printf("%c",str->c);
		str->next=(st*)malloc(sizeof(stringz));
		str=str->next;
		
	}
	str->next=NULL;

//Print
	str =head;
	while(str->next!=NULL)
	{
		printf("%c",str->c);
		str=str->next;
	}

purely dynamic Roll eyes | :rolleyes:

, hey but never mess up trying your own stringz!. If allowed, I suggest you go with std::string.

Press: 1500 to 2,200 messages in just 6 days? How's that possible sir?
Dr.Brad :Well,I just replied to everything Graus did and then argued with Negus for a bit.

C_Zealot30-Apr-07 20:39

30-Apr-07 20:39

Thank you VuNic.

John R. Shaw30-Apr-07 22:37

John R. Shaw

30-Apr-07 22:37

Uhmmm – No!

To use standard C functions – you need to provide the size of the buffer. C does not create or expand buffers for you – you have to request them manually. Normally you can get away with allocating a buffer that is as large as or larger than you expect to need and just make the call one time.

Off the top of my head, if you need something that resembles dynamic allocation in C:

typedef struct st_MyStringBuffer
{
    size_t length;
    char* buffer;
} MyStringBuffer;

int MyBuffer_Init(MyStringBuffer* pMine)
{
    if( pMine )
    {
        memset(pMine, 0, sizeof(MyStringBuffer)); /* clear it */
        return(1);
    }
    return(0);
}

void MyBuffer_Free(MyStringBuffer* pMine)
{
    if( pMine )
    {
        free(pMine->buffer);
        MyBuffer_Init(pMine); /* clear it */
    }
}

char* MyBuffer_AddString(MyStringBuffer* pMine, const char* pStr)
{
    size_t len;
    if( !pMine || !pStr )
        return(NULL); /* error */

    len = strlen(pStr) + 1; /* +1 for '\0' */
    if( !pMine->buffer )
    {
        pMine->buffer = malloc(len);
        if( !pMine->buffer )
            return(NULL); /* error */
        pMine->buffer[0] = '\0'; /* required because of strcat() latter */
        pMine->length = len;
    }
    else
    {
        len += pMine->length; /* new buffer length */
        if( !realloc(pMine->buffer, len) ) /* expand buffer */
            return(NULL); /* error */
        pMine->length = len;
    }
    return strcat(pMine->buffer, pStr);
}

char* YourFunction(/* your arguments */)
{
    char temp_buffer[256];
    MyStringBuffer my_string_buffer;
    MyBuffer_Init(my_string_buffer);
    while( fgets(temp_buffer, 256, file_ptr) )
    {
        if( !MyBuffer_AddString(my_string_buffer, temp_buffer) )
        {
            MyBuffer_Free(my_string_buffer);
            break;
        }
    }
    /* since we are passing ownership to calling function
    ** we do not need to worry about free it here. */
    return( my_string_buffer->buffer );
}

Well that was fun! Wink | ;)

Of course you could eliminate MyStringBuffer and just do esentially the same thing it does in your function. The advantage of a method like this is that now you can reuse MyStringBuffer any where you need to use that functionality, without having to rewrite it each time.

Any way I did not test the code, so I do not know if it works as expected.

Study the code and try to figure out what it is doing and why.

INTP
"Program testing can be used to show the presence of bugs, but never to show their absence."Edsger Dijkstra

C_Zealot30-Apr-07 22:40

30-Apr-07 22:40

Thank you

scanf () loop question.

C_Zealot30-Apr-07 17:24

30-Apr-07 17:24

Hi:

I wanted to read whatever I receive from stdin to stdout and quit the program. Below is my function:

while(scanf("%s", buffer) != EOF) {
for (i = 0; i < strlen(buffer); i++) {
buffer[i] = tolower(buffer[i]);
}
printf("%s ", buffer);
}

The function actually keeps looping forever. It does echo whatever from stdin to stdout, but it does not quit after one go. I am wondering why?

Thank you.

C_Zealot30-Apr-07 17:51

30-Apr-07 17:51

Question withdrawn. I have found a solution.

Eytukan30-Apr-07 21:58

Eytukan

30-Apr-07 21:58

C_Zealot wrote:
I have found a solution

what was it? Unsure | :~

Press: 1500 to 2,200 messages in just 6 days? How's that possible sir?
Dr.Brad :Well,I just replied to everything Graus did and then argued with Negus for a bit.

C_Zealot30-Apr-07 22:29

30-Apr-07 22:29

Hi:

Simply another approach,

I wrote:

gets(buffer); /*Read a string into the buffer*/
for (i = 0; i < strlen(buffer); i++) { /*Convert each char in the string to its low case*/
buffer[i] = tolower(buffer[i]);
}

printf("%s", buffer); /*Print it at once*/

It can be confusing because whoever reads this can not access my whole program.
But my problem was solved.

Thanks

Re: scanf () loop question.

James R. Twine1-May-07 2:34

James R. Twine

1-May-07 2:34

Not sure why noone has mentioned it yet, but if you have it, strlwr(...) is likely a faster/better way to lowercase the string in buffer.

Peace!

-=- James
Please rate this message - let me know if I helped or not!<HR>If you think it costs a lot to do it right, just wait until you find out how much it costs to do it wrong!
Avoid driving a vehicle taller than you and remember that Professional Driver on Closed Course does not mean your Dumb Ass on a Public Road!
See DeleteFXPFiles

David Crow1-May-07 2:16

David Crow

1-May-07 2:16

C_Zealot wrote:
while(scanf("%s", buffer) != EOF) {

scanf() does not operate on stdin. Use fscanf(stdin, ...) for that.

C_Zealot wrote:
The function actually keeps looping forever.

So why aren't you checking to see why that is so?

"A good athlete is the result of a good and worthy opponent." - David Crow

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

Re: scanf () loop question.

James R. Twine1-May-07 2:40

James R. Twine

1-May-07 2:40

DavidCrow wrote:
scanf() does not operate on stdin. Use fscanf(stdin, ...) for that.

Just out of curiosity, which RTL implementation are you using? Smile | :)

Peace!

Re: scanf () loop question.

David Crow1-May-07 2:52

David Crow

1-May-07 2:52

James R. Twine wrote:
Just out of curiosity, which RTL implementation are you using?

I know, it sounds funny, but keeping those two functions straight sometimes requires slightly off-kilter thinking. Roll eyes | :rolleyes:

I've just never considered the keyboard to be standard input. Standard input, to me, has always been something like:

myprog.exe < somefile.dat
or
myprog.exe | someotherprog.exe

I'll go back to sleep now.

"A good athlete is the result of a good and worthy opponent." - David Crow

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

Need some suggestions. C programming

C_Zealot30-Apr-07 16:33