C++ Programming Code Examples
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Create a file comparision utility.
/* Create a file comparision utility. */
#include <iostream>
#include <fstream>
using namespace std;
int main(int argc, char *argv[])
{
register int i;
int numread;
unsigned char buffer1[1024], buffer2[1024];
if(argc!=3) {
cout << "Usage: compfiles <file1> <file2>\n";
return 1;
}
ifstream f1(argv[1], ios::in | ios::binary);
if(!f1) {
cout << "Cannot open first file.\n";
return 1;
}
ifstream f2(argv[2], ios::in | ios::binary);
if(!f2) {
cout << "Cannot open second file.\n";
return 1;
}
cout << "Comparing files...\n";
do {
f1.read((char *) buffer1, sizeof buffer1);
f2.read((char *) buffer2, sizeof buffer2);
if(f1.gcount() != f2.gcount()) {
cout << "Files are of differing sizes.\n";
f1.close();
f2.close();
return 0;
}
for(i = 0; i <f1.gcount(); i++) // compare contents of buffers
if(buffer1[i] != buffer2[i]) {
cout << "Files differ.\n";
f1.close();
f2.close();
return 0;
}
} while(!f1.eof() && !f2.eof());
cout << "Files are the same.\n";
f1.close();
f2.close();
return 0;
}
Check whether eofbit is set. Returns true if the eofbit error state flag is set for the stream. This flag is set by all standard input operations when the End-of-File is reached in the sequence associated with the stream. Note that the value returned by this function depends on the last operation performed on the stream (and not on the next). Operations that attempt to read at the End-of-File fail, and thus both the eofbit and the failbit end up set. This function can be used to check whether the failure is due to reaching the End-of-File or to some other reason.
A program shall contain a global function named main, which is the designated start of the program in hosted environment. main() function is the entry point of any C++ program. It is the point at which execution of program is started. When a C++ program is executed, the execution control goes directly to the main() function. Every C++ program have a main() function.
In C++ programming we are using the iostream standard library, it provides cin and cout methods for reading from input and writing to output respectively. To read and write from a file we are using the standard C++ library called fstream. Let us see the data types define in fstream library is: • ofstream: This data type represents the output file stream and is used to create files and to write information to files. • ifstream: This data type represents the input file stream and is used to read information from files. • fstream: This data type represents the file stream generally, and has the capabilities of both ofstream and ifstream which means it can create files, write information to files, and read information from files.
In computer programming, loops are used to repeat a block of code. For example, when you are displaying number from 1 to 100 you may want set the value of a variable to 1 and display it 100 times, increasing its value by 1 on each loop iteration. When you know exactly how many times you want to loop through a block of code, use the for loop instead of a while loop. A for loop is a repetition control structure that allows you to efficiently write a loop that needs to execute a specific number of times.
Returns the number of characters extracted by the last unformatted input operation performed on the object. The unformatted input operations that modify the value returned by this function are: get, getline, ignore, peek, read, readsome, putback and unget. Notice though, that peek, putback and unget do not actually extract any characters, and thus gcount will always return zero after calling any of them. Declaration for gcount(): streamsize gcount() const; This function does not accept any parameter.
Logical Operators are used to compare and connect two or more expressions or variables, such that the value of the expression is completely dependent on the original expression or value or variable. We use logical operators to check whether an expression is true or false. If the expression is true, it returns 1 whereas if the expression is false, it returns 0. Assume variable A holds 1 and variable B holds 0:
Consider a situation, when we have two persons with the same name, jhon, in the same class. Whenever we need to differentiate them definitely we would have to use some additional information along with their name, like either the area, if they live in different area or their mother's or father's name, etc. Same situation can arise in your C++ applications. For example, you might be writing some code that has a function called xyz() and there is another library available which is also having same function xyz(). Now the compiler has no way of knowing which version of xyz() function you are referring to within your code.
Read block of data. Extracts n characters from the stream and stores them in the array pointed to by s. This function simply copies a block of data, without checking its contents nor appending a null character at the end. If the input sequence runs out of characters to extract (i.e., the end-of-file is reached) before n characters have been successfully read, the array pointed to by s contains all the characters read until that point, and both the eofbit and failbit flags are set for the stream. Internally, the function accesses the input sequence by first constructing a sentry object (with noskipws set to true). Then (if good), it extracts characters from its associated stream buffer object as if calling its member functions sbumpc or sgetc, and finally destroys the sentry object before returning.
In while loop, condition is evaluated first and if it returns true then the statements inside while loop execute, this happens repeatedly until the condition returns false. When condition returns false, the control comes out of loop and jumps to the next statement in the program after while loop. The important point to note when using while loop is that we need to use increment or decrement statement inside while loop so that the loop variable gets changed on each iteration, and at some point condition returns false. This way we can end the execution of while loop otherwise the loop would execute indefinitely. A while loop that never stops is said to be the infinite while loop, when we give the condition in such a way so that it never returns false, then the loops becomes infinite and repeats itself indefinitely.
#include is a way of including a standard or user-defined file in the program and is mostly written at the beginning of any C/C++ program. This directive is read by the preprocessor and orders it to insert the content of a user-defined or system header file into the following program. These files are mainly imported from an outside source into the current program. The process of importing such files that might be system-defined or user-defined is known as File Inclusion. This type of preprocessor directive tells the compiler to include a file in the source code program.
In computer programming, we use the if statement to run a block code only when a certain condition is met. An if statement can be followed by an optional else statement, which executes when the boolean expression is false. There are three forms of if...else statements in C++: • if statement, • if...else statement, • if...else if...else statement, The if statement evaluates the condition inside the parentheses ( ). If the condition evaluates to true, the code inside the body of if is executed. If the condition evaluates to false, the code inside the body of if is skipped.
"Switch statement" is multi-way decision that tests whether an expression 'matches' one of a number of "constant integer", and branches accordingly. 'Switch statement' that allows us
