FILE* tmpfile();

#include 
#include 
#include 

using namespace std;

int main()
{
    FILE *fp;
    fp = tmpfile();
    char writeToFile[50] = "Creating a temporary file";
    
    if (fp==NULL)
    {
        perror("Error creating temporary file");
        exit(1);
    }
    
    fputs(writeToFile,fp);
    rewind(fp);
    
    char readFromFile[50];
    fgets(readFromFile, sizeof(readFromFile), fp);
    cout << readFromFile;
    fclose(fp);
    
    return 0;
}

Creating a temporary file