Ad:

C Discussion Thread
Unsolved
Views: 3570

Nov 18th, 2006

popen and "ls"

Expand Post »

Hey!

Writing a simple client/server in C and I'm currently stuck with getting the results after calling system("ls") so I can send it from server to client.

Since system() returns an int I tried popen() -->

C Syntax (Toggle Plain Text)
	char buffer[1000];
	FILE* myPipe = popen(buf, "r");
	if(myPipe==NULL){
		//errorstuff
	}
	while(fgets(buffer, 1000, myPipe)!=NULL){
		(void) printf("%s \n", buffer);
	}	
	pclose(myPipe);
	char buffer[1000];
	FILE* myPipe = popen(buf, "r");
	if(myPipe==NULL){
		//errorstuff
	}
	while(fgets(buffer, 1000, myPipe)!=NULL){
		(void) printf("%s \n", buffer);
	}	
	pclose(myPipe);

But buffer only contains the last filename listed, not the rest of them. How do I get fgets to copy everything into the buffer?

As always; all help is appreciated! :o)

Last edited by Line; Nov 18th, 2006 at 10:21 pm.

Similar Threads

google "keyword" question in Search Engine Optimization
Windows 2000 Adv Server and "Printing Subsystem" in Windows NT / 2000 / XP

Line

Reputation Points: 14

Solved Threads: 0

Newbie Poster

Offline

12 posts
since Sep 2006

Permalink

Nov 21st, 2006

Re: popen and "ls"

Aki, now I'm one step further, using scandir + I've written in the code for sending one filename at the time to the client, who reads in a loop.

The result from this is the server reading the directory and printing it perfectly, while the client writes the name of the first file in the direcory minus the file type. One the new line all the other filenames are put together, but not with complete names, just some letters...! Example -->
! fil (should be fil.txt)
! klieklieold" (this is the files klient, klient.c + directory old)

The server clearly sends a termination to the client as I've tester just printing to the screen when it enters that method... So I know the client should be able to exit the while-loop...

What's causing this? I'm adding my methods for reading a directory, and hoping someone can find an error there, but I'm starting to worry it might be outside these functions...

C Syntax (Toggle Plain Text)
/*
** SERVER **
*******************/	
 
void skrivLs(int sock){
	char *buffer;	
	int teller,i;
	struct direct **files;
	int file_select();
 
	teller = scandir(".", &files, file_select, alphasort);
 
	// Dersom ingen filer blir funnet */
	if(teller < 0){
		perror("Socket");
		strcpy(buffer, "No such file or directory\n");
		printf("BUF; %s\n", buffer);
		rebruk = write(sock, buffer, sizeof(files));
		if(rebruk < 0){
			perror("write() failed");
			close(lytte_sock);
			close(sock);
			exit(1);
		}
		skrivSlutt();
		exit(0);
	}
 
	i=0;
	while(i<teller){
		i++;
		//Test to see this actually works...
		//printf("%s  ",files[i-1]->d_name);
		//printf("\n"); 
		buffer=files[i-1]->d_name;
		rebruk = write(sock, buffer, sizeof(files));
		if(rebruk < 0){
			perror("write() failed");
			close(lytte_sock);
			close(sock);
			exit(1);
		}
	}
	skrivSlutt(); //method that sends "-1" to the client
	nullBuf(buffer);
}
/*
** SERVER **
*******************/	

void skrivLs(int sock){
	char *buffer;	
	int teller,i;
	struct direct **files;
	int file_select();

	teller = scandir(".", &files, file_select, alphasort);

	// Dersom ingen filer blir funnet */
	if(teller < 0){
		perror("Socket");
		strcpy(buffer, "No such file or directory\n");
		printf("BUF; %s\n", buffer);
		rebruk = write(sock, buffer, sizeof(files));
		if(rebruk < 0){
			perror("write() failed");
			close(lytte_sock);
			close(sock);
			exit(1);
		}
		skrivSlutt();
		exit(0);
	}
	
	i=0;
	while(i<teller){
		i++;
		//Test to see this actually works...
		//printf("%s  ",files[i-1]->d_name);
		//printf("\n"); 
		buffer=files[i-1]->d_name;
		rebruk = write(sock, buffer, sizeof(files));
		if(rebruk < 0){
			perror("write() failed");
			close(lytte_sock);
			close(sock);
			exit(1);
		}
	}
	skrivSlutt(); //method that sends "-1" to the client
	nullBuf(buffer);
}

C Syntax (Toggle Plain Text)
/*
** CLIENT **
*******************/
 
void les(){
	nullBuf(buf); //writing a bunch of nulls to buf if it isn't empty
	while(buf){
		rebruk = read(sock, buf, sizeof(buf));
		if(rebruk<0){
			perror("Read");
			close(sock);
			exit(1);
		}
		if(strcmp(buf, slutt)!=0){ //if server sends "-1"
			printf("! %s\n",buf);
		}else{
			break;
		}
	}
}
/*
** CLIENT **
*******************/

void les(){
	nullBuf(buf); //writing a bunch of nulls to buf if it isn't empty
	while(buf){
		rebruk = read(sock, buf, sizeof(buf));
		if(rebruk<0){
			perror("Read");
			close(sock);
			exit(1);
		}
		if(strcmp(buf, slutt)!=0){ //if server sends "-1"
			printf("! %s\n",buf);
		}else{
			break;
		}
	}
}

Line

Reputation Points: 14

Solved Threads: 0

Newbie Poster

Offline

12 posts
since Sep 2006

Permalink

Nov 21st, 2006

Re: popen and "ls"

how is buf declared in that client function? If buf is declared as char* then sizeof(buf) is always 4 on 32-bit compilers.

Ancient Dragon

Sponsor

Team Colleague

Featured Poster

Reputation Points: 5608

Solved Threads: 2283

Retired and Enjoying Life

Offline

21,961 posts
since Aug 2005

Permalink

Nov 21st, 2006

Re: popen and "ls"

Yes, it is a char*... I tried writing 1000 instead of sizeof(buf), but I got the same result... :o/

Thank you so much for taking a look! :o)

Line

Reputation Points: 14

Solved Threads: 0

Newbie Poster

Offline

12 posts
since Sep 2006

Permalink

Nov 21st, 2006

Re: popen and "ls"

C Syntax (Toggle Plain Text)
		buffer=files[i-1]->d_name;
		rebruk = write(sock, buffer, sizeof(files));
		buffer=files[i-1]->d_name;
		rebruk = write(sock, buffer, sizeof(files));

I think this is also wrong. buffer is a pointer to d_name, but attempting to write sizeof(files) number of bytes. If files is an array of pointers to structures, then sizeof(files) will be 4 * number of pointers in that array. You probably mean this, unless files[i-1]->d_name is also a pointer.

C Syntax (Toggle Plain Text)
buffer=files[i-1]->d_name;
rebruk = write(sock, buffer, sizeof(files[i-1]->d_name));
buffer=files[i-1]->d_name;
rebruk = write(sock, buffer, sizeof(files[i-1]->d_name));

In that case why use buffer at all

C Syntax (Toggle Plain Text)
rebruk = write(sock, files[i-1]->d_name, sizeof(files[i-1]->d_name));
rebruk = write(sock, files[i-1]->d_name, sizeof(files[i-1]->d_name));

If d_name is also a pointer, then you should probably replace the sizeof() with strlen(d_name)+1
In that case why use buffer at all

C Syntax (Toggle Plain Text)
rebruk = write(sock, files[i-1]->d_name, strlen(files[i-1]->d_name)+1);
rebruk = write(sock, files[i-1]->d_name, strlen(files[i-1]->d_name)+1);

Now for the client side:
Since buf is a pointer, did you allocate memory for it, or what does it point to? please post code for this.

Last edited by Ancient Dragon; Nov 21st, 2006 at 10:26 am.

Ancient Dragon

Sponsor

Team Colleague

Featured Poster

Reputation Points: 5608

Solved Threads: 2283

Retired and Enjoying Life

Offline

21,961 posts
since Aug 2005

Permalink

Nov 21st, 2006

Re: popen and "ls"

Aki, looked into this and I'm now using

C Syntax (Toggle Plain Text)
rebruk = write(sock, files[i-1]->d_name, strlen(files[i-1]->d_name)+1);
rebruk = write(sock, files[i-1]->d_name, strlen(files[i-1]->d_name)+1);

Click to Expand / Collapse Quote originally posted by Ancient Dragon ...

Now for the client side:
Since buf is a pointer, did you allocate memory for it, or what does it point to? please post code for this.

char buf[1000]; --> That's all I have with buf, the rest is done by the les() method...

Should I allocate memory for it? if so, how and more importantly; Where would it be natural to do it? *clueless*

Line

Reputation Points: 14

Solved Threads: 0

Newbie Poster

Offline

12 posts
since Sep 2006

Permalink

Nov 21st, 2006

Re: popen and "ls"

>>Should I allocate memory for it
not necessary -- what you posted is ok.

Ancient Dragon

Sponsor

Team Colleague

Featured Poster

Reputation Points: 5608

Solved Threads: 2283

Retired and Enjoying Life

Offline

21,961 posts
since Aug 2005

This thread is more than three months old

No one has posted to this discussion for at least three months. Please let old threads die and do not reply to them unless you feel you have something new and valuable to contribute that absolutely must be added to make the discussion complete. Otherwise, please start a new thread in this forum instead.

Previous Thread in C Forum Timeline: urgent help needed for a beginner

Next Thread in C Forum Timeline: Regexp?

DaniWeb Message

Cancel Changes

User Name
Password