folder parsing (newbie)problem

[oswald.harry]

hi
i am learning to parse directory using dirent.h (using gcc of cygwin
as compiler)and tried to make an array of names of .png files in a
directory
here my problem is with accessing a char* []
I wrote this function

int parsedirectory(char * dirname){
struct dirent **filelist = {0};
char * directory =dirname;
int fcount = -1;
int i = 0;
fcount = scandir(directory, &filelist, 0, alphasort);

if(fcount < 0) {
perror(directory);
return 1;
}

int pngcnt;
pngcnt=0;
for(i = 0; i < fcount; i++) {
//i want to check if filename has a .png in it
if(strstr(filelist->d_name,".png")!=NULL){
++jpgcnt;
}

}
printf("png imgs:%d\n",pngcnt);//this shows totalnumber of .pngs

//then I can create a filenames array of size pngcnt

char* filenames[pngcnt];

//then i want to strcat the foldername with the imagename and add it
to the array
//so each entry in the array will be a string like "F:\code\c\testparse
\man1.png"

//but here i am stuck since the value fcount can't be used to //index
this array
//i tried like this

char fldr[strlen(dirname)];
strcpy(fldr,dirname);
strcat(fldr,"\\");
int j;//this i use to index into filenames[]
j=0;
for(i=0;i<fcount;i++){
if(strstr(filelist->d_name,".png")!=NULL){
char* name; //to make full name of a file
char fldrtemp[strlen(fldr)];
strcpy(fldrtemp,fldr);//so that strcat will not chang fldr
name=strcat(fldrtemp,filelist->d_name);
pngfilenames[j++]=name;
}
}

}

my problem is that when i try to iterate thru pngfilenames using
for(i=0;i<pngcnt;i++){
printf("%s\n",pngfilenames);
}

i get something like
D"
D"
D"
D"
not full path imagefilenames as expected!!
i am not sure if this is the right way..my c learning is in its
infancy so if

anyone can suggest a right way i will be grateful

 

[Pravin Paratey]

On Jan 22, 1:13 pm, (e-mail address removed) wrote:

for(i=0;i<fcount;i++){
if(strstr(filelist->d_name,".png")!=NULL){
char* name; //to make full name of a file
char fldrtemp[strlen(fldr)];
strcpy(fldrtemp,fldr);//so that strcat will not chang fldr
name=strcat(fldrtemp,filelist->d_name);
pngfilenames[j++]=name;
}

<snip>

Declare fldrtemp as

char *fldrtemp = new char[strlen(fldr)]; // or malloc

What's happening is all entries in pngfilenames[] array is pointing to
the same string address. Remember to free the memory when you're done.

 

[Mark Bluemel]

On Jan 22, 1:13 pm, (e-mail address removed) wrote:

for(i=0;i<fcount;i++){
if(strstr(filelist->d_name,".png")!=NULL){
char* name; //to make full name of a file
char fldrtemp[strlen(fldr)];
strcpy(fldrtemp,fldr);//so that strcat will not chang fldr
name=strcat(fldrtemp,filelist->d_name);
pngfilenames[j++]=name;
}

<snip>

Declare fldrtemp as

char *fldrtemp = new char[strlen(fldr)]; // or malloc

If you're writing in standard C you can't use the syntax you've shown
above.

1) new is not part of standard C syntax.
2) "//" for comments is only part of the language at C99, though it is
supported by some compilers at earlier levels.

 

[Ben Bacarisse]

i am learning to parse directory using dirent.h (using gcc of cygwin
as compiler)and tried to make an array of names of .png files in a
directory
here my problem is with accessing a char* []

I can only talk about the C issues. I don't know the directory
functions you are using so I will just assume all that is OK.

I wrote this function

There is quite a lot and it is a bit messy. I will point a few
problems but I may well have missed others. Better layout would help
your readers.

int parsedirectory(char * dirname){
struct dirent **filelist = {0};
char * directory =dirname;
int fcount = -1;
int i = 0;
fcount = scandir(directory, &filelist, 0, alphasort);

if(fcount < 0) {
perror(directory);
return 1;
}

int pngcnt;
pngcnt=0;
for(i = 0; i < fcount; i++) {
//i want to check if filename has a .png in it
if(strstr(filelist->d_name,".png")!=NULL){
++jpgcnt;
}

}
printf("png imgs:%d\n",pngcnt);//this shows totalnumber of .pngs

//then I can create a filenames array of size pngcnt

char* filenames[pngcnt];

What do you plan to do with this array? Since it is local, you can't
ever return (a pointer to) it from this function. A more flexible
function would be able to return the array of names found and that
will require an array with a lifetime longer than a local variable
like this (i.e. a malloc'd array and contents).

//then i want to strcat the foldername with the imagename and add it
to the array
//so each entry in the array will be a string like "F:\code\c\testparse
\man1.png"

//but here i am stuck since the value fcount can't be used to //index
this array
//i tried like this

char fldr[strlen(dirname)];
strcpy(fldr,dirname);
strcat(fldr,"\\");

You made fldr only big enough for the letters in dirname. It must be
big enough to hold the terminating null as well as the \ you then add.

int j;//this i use to index into filenames[]
j=0;
for(i=0;i<fcount;i++){
if(strstr(filelist->d_name,".png")!=NULL){
char* name; //to make full name of a file
char fldrtemp[strlen(fldr)];

Not big enough. You must count the null but also the extra stuff you
are about to add (the d_name).

strcpy(fldrtemp,fldr);//so that strcat will not chang fldr
name=strcat(fldrtemp,filelist->d_name);
pngfilenames[j++]=name;

Here you are setting each array entry to point to a string which will
disappear when the loop body ends which is immediately! You need to
allocate storage for the string using malloc.

}
}

}

The function should new free everything it has allocated. A read of
the C FAQ would help you, I think: http://c-faq.com/

 

[Nick Keighley]

i am learning to parse directory using dirent.h (using gcc of cygwin
as compiler)

technically direct.h is off-topic. If your problem is with
dirent.h you need to take it to a unix news group.

But I'm not sure your problem is dirent.h...

and tried to make an array of names of .png files in a
directory
here my problem is with accessing a char* []
I wrote this function

int parsedirectory(char * dirname){
 struct dirent **filelist = {0};

you've initialised this as if it were a struct.
It's not it's a ptr.

use
struct dirent **filelist = NULL;

 char * directory =dirname;
 int fcount = -1;
 int i = 0;
 fcount = scandir(directory, &filelist, 0, alphasort);

 if(fcount < 0) {
  perror(directory);
  return 1;
 }

 int pngcnt;

you can't mix declarations with statements in C89
(the most portable standard).

 pngcnt=0;
 for(i = 0; i < fcount; i++)  {
//i want to check if filename has a .png in it
if(strstr(filelist->d_name,".png")!=NULL){
   ++jpgcnt;
  }

 }
printf("png imgs:%d\n",pngcnt);//this shows totalnumber of .pngs

//then I can create a filenames array of size pngcnt

char* filenames[pngcnt];

this is an array of char*. Somewhere you must allocate some memory
for these pointers to point to. You don't.

//then i want to strcat the foldername with the imagename and add it
to the array
//so each entry in the array will be a string like
// "F:\code\c\testparse\man1.png"

beware of // comments. They screw up in postings

//but here i am stuck since the value fcount can't be used to
//index this array

I've no idea what this means.

//i tried like this

char fldr[strlen(dirname)];

you can't use strlen() as an array dimension. Does this
even compile? If so you are using a weird compiler.
(maybe gcc not in ANSI mode). Assume dirname is six characters.
Then strlen is 6.

strcpy(fldr,dirname);

oops! dirname actually occupies *7* bytes (one for the nul
char).

strcat(fldr,"\\");

oops!! you now have 8 bytes in your 6 byte array.
Use malloc()

char *fldr = malloc (strlen(dirname) + 2);
if (fldr == 0) abort();

int j; //this I use to index into filenames[]
j=0;
for(i=0;i<fcount;i++){
  if(strstr(filelist->d_name,".png")!=NULL){
     char* name; //to make full name of a file
     char fldrtemp[strlen(fldr)];
     strcpy(fldrtemp,fldr);//so that strcat will not chang fldr
     name=strcat(fldrtemp,filelist->d_name);

more of the same. Also you point name at fldrtemp[]
which disappears at the end of the for loop.
And then probably gets reused on the next iteration.
Use malloc().

char* name = malloc (strlen(fldr) + strlen(filelist->d_name) +
1);
strcpy (fldrtemp, fldr);
name = strcat (fldrtemp,filelist->d_name);

/* or replace the last two lines with
sprintf (name, "%s%s", fldr, filelist->d_name);

     pngfilenames[j++]=name;
   }

}
}

my problem is that when i try to iterate thru pngfilenames using
for(i=0;i<pngcnt;i++){
  printf("%s\n",pngfilenames);

}

i get something like
D"
D"
D"
D"
  not full path imagefilenames as expected!!
i am not sure if this is the right way..my c learning is in its
infancy so if

anyone can suggest a right way i will be grateful

a general suggestion is break the program down into
smaller steps. Write a program then returns all the files
in the directory. Print them out. Does that look ok?
Filter out the pngs. Print them

<OT>
you do know scandir() will do this for you?
</OT>

turn up your compiler warnings. If it's gcc
use
gcc -W -Wall -ansi -pedantic

and maybe -O2

you should probably read up on pointers and on malloc().

char *name[23];

defines an array of pointers. It *does not* allocate
any memory for the pointers to point at.

 

[Keith Thompson]

Declare fldrtemp as

char *fldrtemp = new char[strlen(fldr)]; // or malloc

What's happening is all entries in pngfilenames[] array is pointing to
the same string address. Remember to free the memory when you're done.

Apart from the fact that "new" is C++, not C, you're not allocating
space to hold the terminating '\0'.