How to get file suffix in c++?

Question

I want to get the suffix(.txt,.png etc.) of a file that I know that exists in some folder. I know that the file name(prefix) is unique in this folder. The language is c++.

thanks

Answer 1

Assuming that "suffix" is the filename extension, you can do this:

char * getfilextension(char * fullfilename)
{
   int size, index;
   size = index = 0;

   while(fullfilename[size] != '\0') {
      if(fullfilename[size] == '.') {
         index = size;
      }
       size ++; 
   }

   if(size && index) {
      return fullfilename + index;
   }
      return NULL;
}

It's C code, but I believe that can easily ported to C++(maybe no changes).

getfilextension("foo.png"); /* output -> .png */

I hope this help you.

UPDATE:

You will need scan all files of directory and compare each file without extension if is equal to your target.

    #include <stdio.h>
    #include <unistd.h>
    #include <stdlib.h>
    #include <limits.h>
    #include <dirent.h>
    #include <string.h>

    //.....

    char * substr(char * string, int start, int end)
    {
       char * p = &string[start];
       char * buf = malloc(strlen(p) + 1);
       char * ptr = buf;
       if(!buf) return NULL;

       while(*p != '\0' && start < end) {
          *ptr ++ = *p++;
          start ++;
       }

       *ptr++ = '\0';

       return buf;

    }

    char * getfilenamewithoutextension(char * fullfilename)
    {
       int i, size;
       i = size = 0;

       while(fullfilename[i] != '\0') {
          if(fullfilename[i] == '.') {
             size = i;
          }

          i ++;
       }

       return substr(fullfilename, 0, size);
    }

    char * getfilextension(char * fullfilename)
    {
       int size, index;
       size = index = 0;

       while(size ++, fullfilename[size]) {
          if(fullfilename[size] == '.') {
             index = size;
          }
       }

       if(size && index) {
          return fullfilename + index;
       }
          return NULL;
    }

   char*FILE_NAME;
   int filefilter(const struct dirent * d)
   {
      return strcmp(getfilenamewithoutextension((char*)d->d_name), FILE_NAME) == 0;
   }

and then:

   void foo(char * path, char * target)  {
   FILE_NAME = target;
   struct dirent ** namelist;
   size_t dirscount;
   dirscount = scandir(path, &namelist, filefilter, alphasort);

   if(dirscount > 0) {
      int c;
      for(c = 0; c < dirscount; c++) {
            printf("Found  %s filename,the extension is %s.\n", target, getfilextension(namelist[c]->d_name));
            free(namelist[c]);
      }

      free(namelist);
   } else {
      printf("No files found on %s\n", path);
   }

}

and main code:

int main(int argc, char * argv[])
{

   foo(".", "a"); /* The .(dot) scan the current path */
}

For a directory with this files:

a.c  a.c~  a.out
a.o  makefile test.cs

The output is:

Found  a filename,the extension is .c.
Found  a filename,the extension is .c~.
Found  a filename,the extension is .o.
Found  a filename,the extension is .out.

Note: the scandir() function is part of GNU extensions/GNU library,if you don't have this function available on your compiler,tell me that I will write an alias for that or use this implementation(don't forget to read the license).

Answer 2

If you're using Windows, use PathFindExtension.

Answer 3

There's no standard functionality to list directory contents in c++. So if you know allowed extensions in your app you can iterate through and find if file exists.

Other options are use OS specific API or use something like Boost. You can also use "ls | grep *filename" or "dir" command dump and parse the output.