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@@ -156,41 +156,45 @@ Here’s code using exceptions to sort a collection of lines by slope:
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```cpp
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```cpp
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class Point {
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class Point {
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public:
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public:
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Point(double x_, double y_) : x(x_),y(y_) {}
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Point(double x_, double y_) : x(x_),y(y_) {}
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double x,y;
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double x,y;
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};
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};
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class Line {
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class Line {
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public:
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public:
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Line(const Point &a_, const Point &b_) : a(a_),b(b_) {}
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Line(const Point &a_, const Point &b_) : a(a_),b(b_) {}
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Point a,b;
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Point a,b;
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};
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};
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double compute_slope(const Point &a, const Point &b) throw(int) {
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double compute_slope(const Point &a, const Point &b) throw(int) {
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double rise = b.y - a.y;
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double rise = b.y - a.y;
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double run = b.x - a.x;
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double run = b.x - a.x;
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double epsilon = 0.00001;
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double epsilon = 0.00001;
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if (fabs(run) < epsilon) throw -1;
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if (fabs(run) < epsilon) throw -1;
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return rise / run;
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return rise / run;
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}
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}
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double slope(const Line &ln) {
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double slope(const Line &ln) {
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return compute_slope(ln.a,ln.b);
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return compute_slope(ln.a,ln.b);
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}
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}
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bool steeper_slope(const Line &m, const Line &n) {
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bool steeper_slope(const Line &m, const Line &n) {
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double slope_m = slope(m);
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double slope_m = slope(m);
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double slope_n = slope(n);
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double slope_n = slope(n);
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return slope_m > slope_n;
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return slope_m > slope_n;
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}
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}
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void organize(std::vector<Line> &lines) {
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void organize(std::vector<Line> &lines) {
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std::sort(lines.begin(),lines.end(), steeper_slope);
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std::sort(lines.begin(),lines.end(), steeper_slope);
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}
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}
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int main () {
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int main () {
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std::vector<Line> lines;
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std::vector<Line> lines;
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/* omitting code to initialize some data */
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/* omitting code to initialize some data */
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try {
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try {
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organize(lines);
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organize(lines);
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/* omitting code to print out the results */
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/* omitting code to print out the results */
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} catch (int) {
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} catch (int) {
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std::cout << "error: infinite slope" << std::endl;
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std::cout << "error: infinite slope" << std::endl;
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}
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}
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}
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}
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```
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```
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@@ -206,19 +210,20 @@ type from the exception class, and overwrite the what() member function
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```cpp
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```cpp
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class myexception: public std::exception {
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class myexception: public std::exception {
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virtual const char* what() const throw() {
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virtual const char* what() const throw() {
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return "My exception happened";
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return "My exception happened";
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}
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}
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};
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};
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int main () {
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int main () {
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myexception myex;
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myexception myex;
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try {
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try {
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throw myex;
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throw myex;
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}
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}
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catch (std::exception& e) {
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catch (std::exception& e) {
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std::cout << e.what() << std::endl;
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std::cout << e.what() << std::endl;
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}
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}
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return 0;
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return 0;
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}
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}
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```
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```
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- The STL library throws several different types of exceptions (all derived from the STL exception class):
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- The STL library throws several different types of exceptions (all derived from the STL exception class):
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@@ -239,10 +244,10 @@ allocate sufficient memory resources for the object, the bad alloc exception is
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```cpp
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```cpp
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try {
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try {
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int* myarray= new int[1000];
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int* myarray= new int[1000];
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}
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}
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catch (std::exception& e) {
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catch (std::exception& e) {
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std::cout << "Standard exception: " << e.what() << std::endl;
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std::cout << "Standard exception: " << e.what() << std::endl;
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}
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}
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```
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```
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- It can also be useful to have the constructor for a custom class throw a descriptive exception if the arguments
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- It can also be useful to have the constructor for a custom class throw a descriptive exception if the arguments
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