202308201250
Status: #idea
Tags: OS

C Programs (Misc.)

Memory Protection

int x;
scanf("%d", &x); // Takes an address
printf("%d", x); // Takes a value

scanf("%d", x); // Seg fault: Probably an address outside the program's block

int A[10];
// Something... int x;
printf("%d", A[11]); // Seg fault: If A is last address in block
// Could print garbage value, at address of x

int x;
printf("%d", 5); // May not be visible. Need to flush buffers to guarantee display

fflush(stdout); // Flushes stdout

scanf("%d", x); // Segfault

Linking libraries

• Header files only the interface to interact with the library, i.e. the function declarations
• Implementation of the header files are stored in static library .a files, or dynamic .so shared object files.
  • Advantage of .so files is that you don't need to recompile your main code, if there is a change in the shared object file, as long as it is linked to the new shared object file

Taking input

• Generally, programs take multi-character input.
• The keyboard however, is an ASCII single-character input device
• The OS handles taking multiple characters of inputs, and converting it to an integer and providing it to the program running below

#include <stdio.h>
int x;
scanf("%d", x);

References

1. scanf
2. fflush