Laboratory Exercises, C++ Programming

Tools for Practical C++ Development 19
==2938== by 0x41A5DE6: strtol (strtol.c:110)
==2938== by 0x41A3160: atoi (atoi.c:28)
==2938== by 0x80486B9: main (reciprocal.cc:9)
==2938== Address 0x0 is not stack’d, malloc’d or (recently) free’d
==2938== ...
==2938==
==2938== HEAP SUMMARY:
==2938== in use at exit: 0 bytes in 0 blocks
==2938== total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==2938==
==2938== All heap blocks were freed -- no leaks are possible
==2938==
==2938== For counts of detected and suppressed errors, rerun with: -v
==2938== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 17 from 6)
[1] 2938 segmentation fault valgrind --leak-check=yes ./reciprocal
When the error occurs, you get an error message and a stack trace (and a lot of other information).
In this case, it is almost the same information as when you used gdb, but this is only because the
error resulted in a segmentation violation. But most errors don’t result in immediate traps:
void zero(int* v, size_t n) {
for (size_t i = 0; i < n; ++i)
v[i] = 0;
}
int main() {
int* v = new int[5];
zero(v, 10); // oops, should have been 5
// ... this error may result in a trap now or much later, or wrong results
}
A6. The file vgtest.cc contains a test program with two functions with common programming
errors. Write more functions to check other common errors. Note that valgrind cannot find
addressing errors in stack-allocated arrays (like int v[10]; v[10] = 0). Run the program
under valgrind, try to interpret the output.
Advice: always use valgrind to check your programs! Note that valgrind may give
“false” error reports on C++ programs that use STL or C++ strings. See the valgrind FAQ,
http://valgrind.org/docs/manual/faq.html#faq.reports
4 Makefiles and Topological Sorting
4.1 Introduction
Targets and prerequisites of a makefile form a graph where the vertices are files and an arc
between two vertices corresponds to a dependency. When make is invoked, it computes an order
in which the files are to be compiled so the dependencies are satisfied. This corresponds to a
topological sort of the graph.
Consider a simplified makefile containing only implicit rules, i.e., lines reading target:
prerequisites. You are to implement a C++ program topsort that reads such a file, whose name
is given on the command line, and outputs the targets to standard output in an order where
the dependencies are satisfied. If the makefile contains syntax errors or cyclic dependencies, the
program should exit with an error message.
This is not a trivial task. The solution will be developed stepwise in the following sections.