file existence check and ask if aleady exist to make another file name

Hi...
i have this code to check if file exist already and its work,
but what i need is : is to add feature to function to see if the file already exist open same file and rename it with another name ,probably file2

assume file name is "abc.c"
this scenario like this

User>>(provide file name)

Code>>(check if file already exist show msg:

"File already (abc.c) exist would you like to create another file and rename it ("abc2.c") "maybe it need loop to search directory "????

User>>if press yes ok it will make another file with another name
but if no exit the function and dont create another file

Code:

---

// function to check file existence and here what i need to add the feature above

int fExist(const char* fn){
    struct stat buffer;
    int exist = stat(fn,&buffer);
    if(exist == 0)
        return 1;
    else // -1
        return 0;
}

---

and here is in the main():

Code:

---

int exist = fExist(filename);
                        if(exist)
                        {
                            printf("File already (%s) exist.\n",filename);
                            continue;
                        }
                        else
                        {
                            fd=open(filename,O_WRONLY |O_CREAT,mode);                   
                            printf("FIle is being downloaded ...\n");
                       
                            /* write the data from file to buffer    */                       
                            write(fd,buffer,sizeof(char)*strlen(buffer));           
                            printf("Finish downloading....\n");
                            printf(".....................................................\n");
                        }

---

Popping up a message sounds like it just adds more potential for this to screw up.
While the message box is open the user could manually create a file with the new suggested name, or delete or rename the original file. I recommend that you don't show a message until after you've done it, informing the user of what you have done.

If you can use open(3) you might want to consider using O_CREAT and O_EXCL together, which will cause the call to open to fail if it already exists, making the "check for existence" part and the "create the file" part an atomic operation. See Man Page for open (freebsd Section 2) - The UNIX and Linux Forums for details

The reason this is important on multi-user systems is because the following incorrect behavior is possible:

1. Your program uses stat to see if `foo' exists and finds that it doesn't
2. Some other program creates `foo', unknown to your program
3. Your program overwrites `foo' because it still thinks from step 1 that it doesn't exist