C - listing files contained in folder and all subfolders - c

Question

I have a function that reads all files contained in a single input directory.
I wanted to make that function read not only files in "main" directory, but also ones contained in all subdirectories.
In order to do so, i wrote this code:
#include <sys/types.h>
#include <dirent.h>
#include <errno.h>
#include <stdio.h>
struct dirent *readdir(DIR *dirp);
char * percorso;
DIR *cartella;
struct dirent *elemento;
char * scrivi(char * a, char * b)
{
char *targetdir = malloc(2048);
strcpy(targetdir,a);
strcat(targetdir,"/");
strcat(targetdir,b);
printf("%s \n", targetdir);
return targetdir;
}
void scorriFolder(char* nome)
{
if ((cartella = opendir(nome)) == NULL)
perror("opendir() error");
else {
printf("contents of root: \n");
while ((elemento = readdir(cartella)) != NULL)
{
if(elemento->d_type == DT_DIR)
{
if(elemento->d_name != ".." || elemento->d_name != ".")
{
percorso = scrivi(nome, elemento->d_name);
scorriFolder(percorso);
}
}
else
{
printf(" %s\n", elemento->d_name);
}
}
closedir(cartella);
}
}
main(int argc, char * argv[]) {
scorriFolder(argv[1]);
}
But it doesn't even compile, saying:
warning: incompatible implicit declaration of built-in function ‘malloc’
warning: incompatible implicit declaration of built-in function ‘strcpy’
warning: incompatible implicit declaration of built-in function ‘strcat’
As far as I know, this issue is due to a wrong format of variables passed into malloc, strcpy and strcat functions. (elemento->d_name has type char and not char*
What can I do, in order to get this code work?
Thanks.
EDIT
This is a working while snippet:
while ((elemento = readdir(cartella)) != NULL)
{
if ( strcmp(elemento->d_name, ".") == 0)
{
continue;
}
if ( strcmp(elemento->d_name, "..") == 0)
{
continue;
}
if(elemento->d_type == DT_DIR)
{
{
percorso = scrivi(nome, elemento->d_name);
scorriFolder(percorso);
}
}
else
{
printf(" %s\n", elemento->d_name);
}
}
Once it scans a subdirectory it crashes because path it is not updated as the program exits from subdirectory. I am trying to fix it.

Answer 1

You need to add #include <stdlib.h> and #include <string.h> to the beginning of the file.
warning: incompatible implicit declaration of built-in function ‘malloc’
This error message is telling you that the compiler can't determine the return type and parameters to malloc. I think the compiler assumes int for the return type if it can't find one. Which is not void * which malloc actually returns.
malloc is defined in <stdlib.h>
strcpy and strcat are defined in <string.h>
To find out where these functions are defined you can read the man page by typing man malloc , man strcpy, or man strcat