Producing a random file name, and then creating the file, In C++ - c++

Question

In my program, I'm attempting to Generate a random file name, and then use fopen to create a file with that name. The process goes as following
Create a random file name
Check if we are administrator by attempting to create a file with that name in c:\
Write stuff to the file
The function I use to make the random file name is:
const char *RandomName(const char *suffix,unsigned int length)
{
const char alphanum[] =
"0123456789"
"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
"abcdefghijklmnopqrstuvwxyz";
int stringLength = sizeof(alphanum) - 1;
std::string Str;
unsigned int i;
Str.append("c:\\");
for( i = 0; i < length; ++i)
{
Str += alphanum[rand() % stringLength];
}
Str += suffix;
const char *str =Str.c_str();
return str;
}
The function I use to create the file, and check for Admin is:
bool IsAdmin()
{
const char *n = RandomName(".BIN",5);
cout << n << endl;
FILE *fp;
fp = fopen((const char *)n,"w+");
if (fp == NULL) {
cout << "File pointer was NULL" << endl;
return false;
} else {
cout << "File pointer is legit" << endl;
//fclose(fp);
//remove(n);
int b;
for(b = 0; b != 1338; b++)
{
char f = 'c';
fputc(f, fp);
}
return true;
}
}
When run as Admin, The program prints:
c:\9UswA.BIN
Not Admin!
How do I get the program to create a file with a name that matches what it shows on screen? and without sketchy behavior?

Answer 1

Simple
just use tmpnam c api
example:
#include <stdio.h>
int main(void)
{
char name[40];
int i;
for(i=0; i<3; i++) {
tmpnam(name);
printf("%s ", name);
}
return 0;
}

Answer 2

I think running the .exe created here as administrator would let you create the file.
Run the program not from any IDE but manually from file location and run as admin.

Answer 3

To solve the problem, I got rid of the RandomName function and edited IsAdmin to include its code, with a few tweaks I was able to get it to work at least somewhat well, the code I ended up with was:
void AdminWrite(const char *suffix,unsigned int length)
{
FILE *fp;
const char alphanum[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuv";
int stringLength = sizeof(alphanum) - 1;
std::string Str;
unsigned int i;
Str.append("c:\\Users\\UserName\\Desktop\\");
for( i = 0; i < length; ++i)
{
Str += alphanum[rand() % stringLength];
}
Str += suffix;
const char *str =Str.c_str();
cout << str << endl;
fp = fopen(str,"w+");
if (fp == NULL) {
cout << "File pointer was NULL" << endl;
return;
} else {
cout << "File pointer is legit" << endl;
int b;
for(b = 0; b != 1337; b++)
{
char f = 'c';
fputc(f, fp);
}
return;
}
return;
}