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Without changing any variable names, modify bar5.c on page 666 so that foo5.c prints the correct values of x and y (i.e., the hex representations of integers 15213 and 15212).

Without changing any variable names, modify bar5.c on page 666 so that foo5.c prints the correct values of x and y (i.e., the hex representations of integers 15213 and 15212).

Computer Networking: A Top-Down Approach (7th Edition)
Computer Networking: A Top-Down Approach (7th Edition)
7th Edition
ISBN:9780133594140
Author:James Kurose, Keith Ross
Publisher:James Kurose, Keith Ross
Chapter1: Computer Networks And The Internet
Section: Chapter Questions
Problem R1RQ: What is the difference between a host and an end system? List several different types of end...
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666 Chapter 7 Linking 1 /* foo5.c */ 1 /* bar5.c */ 2 #include <stdio.h> 2 double x; 3 void f(void); 3 4 4 void f() 5 int x = 15213; 5 { int y 15212; 6 -0.0; %D 7 7 8 int main () { 10 f(); Ox%x y Ox%x \n", printf ("x х, у); 11 %3D 12 13 return 0; 14 } On an IA32/Linux machine, doubles are 8 bytes and ints are 4 bytes. Thus the assignment x = -0.0 in line 6 of bar5.c will overwrite the memory locations for x and y (lines 5 and 6 in foo5.c) with the double-precision floating-point representation of negative zero! linux> gcc -o foobar5 foo5.c bar5.c linux> ./foobar5 x = Ox0 y Ox80000000 This is a subtle and nasty bug, especially because it occurs silently, with no warning from the compilation system, and because it typically manifests itself much later in the execution of the program, far away from where the error occurred. In a large system with hundreds of modules, a bug of this kind is extremely hard to fix, especially because many programmers are not aware of how linkers work. When in doubt, invoke the linker with a flag such as the Gcc -fno-common flag, which triggers an error if it encounters multiply defined global symbols. 7.7 Without changing any variable names, modify bar5.con page 666 so that foo5.c prints the correct values of x and y (i.e., the hex representations of integers 15213 and 15212).
Transcribed Image Text:666 Chapter 7 Linking 1 /* foo5.c */ 1 /* bar5.c */ 2 #include <stdio.h> 2 double x; 3 void f(void); 3 4 4 void f() 5 int x = 15213; 5 { int y 15212; 6 -0.0; %D 7 7 8 int main () { 10 f(); Ox%x y Ox%x \n", printf ("x х, у); 11 %3D 12 13 return 0; 14 } On an IA32/Linux machine, doubles are 8 bytes and ints are 4 bytes. Thus the assignment x = -0.0 in line 6 of bar5.c will overwrite the memory locations for x and y (lines 5 and 6 in foo5.c) with the double-precision floating-point representation of negative zero! linux> gcc -o foobar5 foo5.c bar5.c linux> ./foobar5 x = Ox0 y Ox80000000 This is a subtle and nasty bug, especially because it occurs silently, with no warning from the compilation system, and because it typically manifests itself much later in the execution of the program, far away from where the error occurred. In a large system with hundreds of modules, a bug of this kind is extremely hard to fix, especially because many programmers are not aware of how linkers work. When in doubt, invoke the linker with a flag such as the Gcc -fno-common flag, which triggers an error if it encounters multiply defined global symbols. 7.7 Without changing any variable names, modify bar5.con page 666 so that foo5.c prints the correct values of x and y (i.e., the hex representations of integers 15213 and 15212).
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