C++ Tutorial/Exceptions/try catch

A simple exception handling example

<source lang="cpp">#include <iostream> using namespace std; int main() {

 cout << "Start\n";
 try {
   cout << "Inside try block\n";
   throw 1;                          // throw an error
   cout << "This will not execute";
 }
 catch (int i) {                       // catch an error
   cout << "Caught an exception -- value is: ";
   cout << i << "\n";
 }
 cout << "End";
 return 0;

}</source>

Start
Inside try block
Caught an exception -- value is: 1
End"

A try block can be localized to a function

<source lang="cpp">#include <iostream> using namespace std;

void f(int test) {

 try{ 
   if(test) throw test; 
 } 
 catch(int i) { 
   cout << "Caught One!  Ex. #: " << i << "\n"; 
 } 

}

int main() {

 cout << "start\n"; 

 f(1); 
 f(2); 
 f(0); 
 f(3); 

 cout << "end"; 

 return 0; 

}</source>

start
Caught One!  Ex. #: 1
Caught One!  Ex. #: 2
Caught One!  Ex. #: 3
end

Catch all exceptions

<source lang="cpp">#include <iostream> using namespace std;

void f(int test) {

 try{ 
   if(test==0) throw test; // throw int 
   if(test==1) throw "a"; // throw char 
   if(test==2) throw 123.23; // throw double 
 } 
 catch(...) { // catch all exceptions 
   cout << "Caught One!\n"; 
 } 

}

int main() {

 f(0); 
 f(1); 
 f(2); 

 return 0; 

}</source>

Caught One!
Caught One!
Caught One!

Catch "char *" exception

<source lang="cpp">#include <iostream.h> int main () {

 try
 {
     throw "Out of range";
 }
 catch (char * str)
 {
   cout << "Exception: " << str << endl;
 }
 return 0;

}</source>

This application has requested the Runtime to terminate it in an unusual way.
Please contact the application"s support team for more information.

Catching derived classes

<source lang="cpp">#include <iostream> using namespace std; class B { }; class D: public B { }; int main() {

 D derived;
 try {
   throw derived;
 }
 catch(B b) {
   cout << "Caught a base class.\n";
 }
 catch(D d) {
   cout << "This won"t execute.\n";
 }
 return 0;

}</source>

Multiple catch blocks

<source lang="cpp">#include <iostream.h> int main () {

 try
 {
   char * mystring;
   mystring = new char [10];
   if (mystring == NULL) 
      throw "Allocation failure";
   
   for (int n=0; n<=100; n++)
   {
     if (n>9) 
        throw n;
     mystring[n]="a";
     
   }
 }
 catch (int i)
 {
   cout << "index " << i << " is out of range" << endl;
 }
 catch (char * str)
 {
   cout << "Exception: " << str << endl;
 }
 return 0;

}</source>

index 10 is out of range

Throwing an exception from a function called from within a try block

<source lang="cpp">#include <iostream> using namespace std;

void f(int test) {

 cout << "Inside f, test is: " << test << "\n"; 
 if(test) 
    throw test; 

}

int main() {

 cout << "start\n"; 

 try { // start a try block 
   cout << "Inside try block\n"; 
   f(0); 
   f(1); 
   f(2); 
 } 
 catch (int i) { // catch an error 
   cout << "Caught an exception -- value is: "; 
   cout << i << "\n"; 
 } 

 cout << "end"; 

 return 0; 

}</source>

start
Inside try block
Inside f, test is: 0
Inside f, test is: 1
Caught an exception -- value is: 1
end

try catch block without exception being thrown

<source lang="cpp">#include <iostream> using namespace std; int main() {

 cout << "Start\n";
 try { 
   cout << "Inside try block\n";
   cout << "Still inside try block\n";
 }
 catch (int i) {
   cout << "Caught an exception -- value is: ";
   cout << i << "\n";
 }
 cout << "End";
 return 0;

}</source>

Start
Inside try block
Still inside try block
End"

Use catch(...) as a default

<source lang="cpp">#include <iostream> using namespace std; void f(int val) {

 try{
   if(val==0) 
      throw val;
   if(val==1) 
      throw "a";
   if(val==2) 
      throw 123.23;
 }
 catch(int i) {                      // catch an int exception
   cout << "Caught an integer\n";
 }
 catch(...) {                        // catch all other exceptions
   cout << "Caught One!\n";
 }

} int main() {

 f(0);
 f(1);
 f(2);
 return 0;

}</source>

Caught an integer
Caught One!
Caught One!

Use multiple catch statements

<source lang="cpp">#include <iostream> using namespace std;

void f(int test) {

 try{ 
   if(test) 
      throw test;            // throw int 
   else 
      throw "Value is zero"; // throw char * 
 } 
 catch(int i) { 
   cout << "Caught One!  Ex. #: " << i << "\n"; 
 } 
 catch(char *str) { 
   cout << "Caught a string: "; 
   cout << str << "\n"; 
 } 

}

int main() {

 cout << "start\n"; 

 f(1); 
 f(2); 
 f(0); 
 f(3); 

 cout << "end"; 

 return 0; 

}</source>

start
Caught One!  Ex. #: 1
Caught One!  Ex. #: 2
This application has requested the Runtime to terminate it in an unusual way.
Please contact the application"s support team for more information.