How to do remove the last occurrence of a string from another string?

Question

Say I have to remove the last occurrence of a string from another string. How would I go about it?

To elaborate, I have a file name in ac string (gchar* or char* )

C:\\SomeDir\\SomeFolder\\MyFile.pdf

and I want to remove the extension .pdf , and change it to something else, eg .txt or .png . What is the least troublesome yet efficient , convenient and cross-platform way to do it? Thanks.

note : I know this is an extremely simple thing to do in C++ but for this project , I absolutely MUST use C and no other language. (academic requirement)

note 2 : Although you can suggest other third-party library , I currently only have access to the C standard library and the GLib.

note 3 : I have searched for similar questions with the "C" tag, but can't seem to find any.

Answer 1

have a look at basename.

NAME
dirname, basename - Parse pathname components

SYNOPSIS
#include <libgen.h>

char *dirname(char *path);
char *basename(char *path);

DESCRIPTION
Warning: there are two different functions basename() - see below.
The functions dirname() and basename() break a null-terminated
pathname string into directory and filename components. In the
usual case, dirname() returns the string up to, but not including,
the final ’/’, and basename() returns the component following the
final ’/’. Trailing ’/’ characters are not counted as part of the
pathname.

Answer 2

I would normally use the "splitpath" function to seperate all four parts of a full path name (dir, path, name, ext). Best regards Oliver

Answer 3

char fil[] = "C:\\SomeDir\\SomeFolder\\MyFile.pdf";
char fil2[1000];
char extension[] = ".tmp";

// search for . and add new extension
sprintf(fil2, "%s%s", strtok(fil, "."), extension);
printf("%s\n", fil2);

Answer 4

Just modifying the above 'strtok' code with 'strrchr' function

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#define MAX_PATH 255

int main() 
{
  char f[MAX_PATH] = "dir\\file.pdf";
  char f1[MAX_PATH];
  char ext[] = ".tmp";
  char *ptr = NULL;
  // find the last occurance of '.' to replace
  ptr = strrchr(f, '.');
  // continue to change only if there is a match found
  if (ptr != NULL) {
    snprintf(f1, (ptr-f)+1, "%s", f);
    strcat(f1, ext);
  }
  printf("%s\n", f1);
  return 1;
}