Continuing from the comments in this idea: http://forums.ni.com/t5/LabVIEW-Idea-Exchange/Access-to-console-output/idc-p/1768066 here's a set of VIs that let you get stuff you write to stderr and stdout in a dll loaded by LabVIEW into LabVIEW. It basically works by redirecting these std ios through a pipe and reading the pipe in LabVIEW.
For stderr and stdout, just run the "example output" VI and while that is running write to stdout or stderr from a dll loaded in LabVIEW like the following code or using the "STD write" VI and it'll show up in the "example output" VI's indicator.
extern "C" __declspec(dllexport) void __stdcall STDerr(char * str)
{
fprintf(stderr, "%s\n", str);
fflush(stderr);
}
Note, I had to add both a new line and fflush, otherwise it didn't consistently get to LabVIEW.
Now, for stdin I was having a bit of trouble. Doing the same thing (running the "example input" VI) resulted in a string control not being read in the loop. Just run the "example input" VI and while it's running change the "string to write" control to different text and you'll see that the new text will only be written after you press the stop button which doesn't make any sense.
The second issue I had was when I tried to read stdin from the dll loaded by LabVIEW. Even with trying AllocConsole() I always got EOF (e.g. when calling getchar(), see the code) independently of the VIs, it just seemed that stdin was disabled so I couldn't read from it, yet AllocConsole should have enabled it but it didn't. Also, printing to the console didn't actually display anything on the console. This may have something to do with this thread: http://forums.ni.com/t5/LabVIEW/using-stdin-stdout-with-LabVIEW/td-p/361573
Anyway, I if someone can get stding to work, I imagine they would be able to use the second set of VIs to write into stdin from LabVIEW and read it in the dll.
//AllocConsole();
FILE* f;
fopen_s(&f, "test stdin.txt", "w");
for (int i= 0;i<100;++i)
{
fprintf(f, "%d\n", getchar());
}
//FreeConsole();
fclose(f);
I updated the string control to new text, but I never clicked out of the string control until I clicked the stop button so the new string only got read when I hit the stop button 
I didn't realize/forgot that the string control only updates to the new text once you click out of it. So it does work as expected.
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