Question

C’s memory model, with its use of pointer arithmetic and all, seems to model flat address space. 16-bit computers used segmented memory access. How did 16-bit C compilers deal with this issue and simulate a flat address space from the perspective of the C programmer? For example, roughly what assembly language instructions would the following code compile to on an 8086?

long arr[65536];  // Assume 32 bit longs.
long i;
for(i = 0; i < 65536; i++) {
    arr[i] = i;
}

Answer 1

How did 16-bit C compilers deal with
this issue and simulate a flat address
space from the perspective of the C
programmer?

They didn’t. Instead, they made segmentation visible to the C programmer, extending the language by having multiple types of pointers: near, far, and huge. A near pointer was an offset only, while far and huge pointers were a combined segment and offset. There was a compiler option to set the memory model, which determined whether the default pointer type was near or far.

In Windows code, even today, you’ll often see typedefs like LPCSTR (for const char*). The “LP” is a holdover from the 16-bit days; it stands for “Long (far) Pointer”.