variable scope

[Joseph]

Hi all,

I am writting a program which loops each sub-dir inside the /proc and
output the "exe" symbolic link using readlink() ,but I have a problem
with the output .I think it's the problem of variable's scope but I have
no idea how to deal with that.Any one could help me with that?


=============== ===========
#include <fstream>
#include <assert.h>
#include <dirent.h>
#include <stdio.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>
#include <bitset>
#include <iostream>
#include <list>
using namespace std;
int main (int argc, char* argv[]){
char* dir_path;
DIR* dir;
struct dirent* entry;
char entry_path[PATH_MAX + 1];
size_t path_len;
pid_t pid;
dir = opendir ("/proc/");
while ((entry = readdir (dir)) != NULL) {
const char* type;

strncpy (entry_path + path_len, entry->d_name, sizeof (entry_path) -
path_len);
const char* name;
name=entry->d_name;

if(strspn(name, "0123456789")== strlen(name))
{
char proc_path[7]="/proc/";
strcat(proc_pat h,entry_path);
strcat(proc_pat h,"/exe");
int temp=strlen(pro c_path);
printf("%s\n",p roc_path);
proc_path[temp+1]='\0';
char exec_name[PATH_MAX];
readlink(proc_p ath,exec_name,s izeof(exec_name ));
printf("%s\n",e xec_name);

}
}
return 0;
}



=============== ===========


the problem is on "exec_name" ,I think.every time,if it reads a shorter
string into exec_name,then ,the previous longer string left a "tail"
inside it.

How could I fix it?





Thanks a lot!
Joseph

[Victor Bazarov]

Re: variable scope

Joseph wrote:[color=blue]
> I am writting a program which loops each sub-dir inside the /proc and
> output the "exe" symbolic link using readlink() ,but I have a problem
> with the output .I think it's the problem of variable's scope but I have
> no idea how to deal with that.Any one could help me with that?
>
>
> =============== ===========
> #include <fstream>
> #include <assert.h>
> #include <dirent.h>
> #include <stdio.h>
> #include <string.h>
> #include <sys/stat.h>
> #include <sys/types.h>
> #include <unistd.h>
> #include <stdlib.h>
> #include <bitset>
> #include <iostream>
> #include <list>
> using namespace std;
> int main (int argc, char* argv[]){
> char* dir_path;
> DIR* dir;
> struct dirent* entry;
> char entry_path[PATH_MAX + 1];[/color]

Are you sure that 'PATH_MAX + 1' is enough? Besides, your array is
uninitialised. I'd do

char entry_path[PATH_MAX + 1] = {0};
[color=blue]
> size_t path_len;
> pid_t pid;
> dir = opendir ("/proc/");
> while ((entry = readdir (dir)) != NULL) {
> const char* type;[/color]

What's that for?
[color=blue]
>
> strncpy (entry_path + path_len, entry->d_name, sizeof (entry_path) -
> path_len);[/color]

Shouldn't this be

strcpy(entry_pa th + path_len, entry->d_name);

?

I think that's what you're trying to do here, but I don't think you got
the size correctly. Otherwise, if you think you did get the size right,
you still need to zero-terminate the array after you copied.
[color=blue]
> const char* name;
> name=entry->d_name;
>
> if(strspn(name, "0123456789")== strlen(name))
> {
> char proc_path[7]="/proc/";
> strcat(proc_pat h,entry_path);[/color]

'proc_path' is only SEVEN chars. Where is the catenated part stored?
[color=blue]
> strcat(proc_pat h,"/exe");[/color]

Again, you're appending more stuff there. Where does it get stored?

Why are you not using 'std::string' here?
[color=blue]
> int temp=strlen(pro c_path);
> printf("%s\n",p roc_path);
> proc_path[temp+1]='\0';
> char exec_name[PATH_MAX];
> readlink(proc_p ath,exec_name,s izeof(exec_name ));
> printf("%s\n",e xec_name);
>
> }
> }
> return 0;
> }
>
>
>
> =============== ===========
>
>
> the problem is on "exec_name" ,I think.every time,if it reads a shorter
> string into exec_name,then ,the previous longer string left a "tail"
> inside it.
>
> How could I fix it?[/color]

Stop using pointers to char and switch to 'std::string'.

V