stdin or a file

In C i was able to do things like...

Code:

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FILE* file_in;
file_in = stdin;

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And then if i want to actually read from a file i just change what file_in is pointing at. When i try to do this in C++ i just get a bunch of errors that i cant read. Is there a way to do this in C++?

Maybe I'm missing something, but this works in C++.

PHP Code:

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FILE* file_in;
char test[256];
file_in = stdin;
fgets(test,256,file_in);
printf("%s",test);
file_in = fopen("file.txt","r");
fgets(test,256,file_in);
printf("%s",test);
fclose(file_in); 


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You are missing something. Thats C code. I want to use C++. C++ is based on C. Every C program will compile in C++.