Strings & Text File Input

CIS 230

15-Feb-06

Quiz

1. Write a function Prototype for the function swap_values that takes two integers by reference and does not return.

2. Write a function call for swap_values. Use the values num1, num2 as arguments.

3. Write a function header for the function swap_values that takes three integers, num1, num2 and does not return.

Strings

• #include <string>

• Character sequence enclosed in double quotes

Declaring & Initializing Strings

• string objectName = value;– string str1 = “Good Morning”;– string str2 = str1;– string str3 = str1 + str2;

• string objectName(stringValue);– string str4(“Hot”);– string str5(str4 + “ Dog”);

• string objectName(str, n);– string str6(“Good Morning”);– string str7(str6, 5); //str7 = “Morning”;

Declaring & Initializing Strings

• string objectName(str, n, p);– string str8(“Good Morning”);– string str9(str8, 5, 2); //str9 = “Mo”;

• string objectName(n, char);– string str10(5, ‘*’); //str10 = “*****”;

• string objectName;– string message; //message = “”;

String Input

string message;

cin >> message;

cout << message;

This may have problems….

Extraction Operator >>

• >> skips any leading whitespace characters

• >> stops at (before) the first trailing whitespace character

• trailing whitespace character is left in stream, and will become “next” leading whitespace character.

String Input Using >>

string firstName;

string lastName;

cin >> firstName >> lastName;

• Input stream:

Joe Hernandez 23

Results:“Joe” “Hernandez”firstName lastName

getline() Function

• >> cannot be used to input a string with blanks in it.

• Use getline(inFileStream, str)

• First argument is an input stream variable (cin), second is the string variable.

string message;

getline(cin, message);

getline(inFileStream, str)

• getline does not skip leading whitespace characters

• getline reads all characters (including blanks) into the string.

• getline stops when it reaches ‘\n’

• ‘\n’ is not stored in the string variable

String Input: getline

string firstName;

string lastName;

getline (cin, firstName);

getline (cin, lastName);

• Input stream:

Joe Hernandez 23

Results:

“Joe Hernandez 23” ?firstName lastName

String Operations

Text File Input

• Text file is an ASCII file

• Handles:– Integers– Floating point numbers– Characters

Text File Input

• #include <fstream>

• Declare a local filename, of type fstream:Examples:

fstream fileName;

fstream inFile;

Commands

• fileName.open(“actualName.dat”, ios::in);

• fileName.eof()

• fileName >> var;

• var = filename.get();

• filename.close();

Makes the connection Tells it’s for input

// Returns true when it reaches the end of file

// Just like cin, except from the file// (>> skips white spaces for char input)

// for char input, includes white spaces

// Closes an opened file

Example: Integer file#include <iostream>#include <fstream>using namespace std;int main(){ int a; fstream inFile; inFile.open(“int.dat”, ios::in); cout << “The values in the file were\n”; while (!inFile.eof()) { inFile >> a; cout << a << “ “; } cout << “\nend of file\n”; inFile.close();}

int.dat345456213578

98222865909145

500<eof>

Output:The values in the file were345 456 213 578 98 222 865 909 145 500end of file

Example: String as Filename#include <iostream>#include <fstream>#include <string>using namespace std;int main(){ int a; string fileName = “int.dat”; fstream inFile; inFile.open(inFile.c_str(), ios::in); … inFile.close();}

Mixed Data

• Input must match the file layout

Example file:

3124 Hammer 12.95

2784 HandSaw 19.99

1447 Wrenches 7.63

integer string float2 spaces 1 space

int main(){ int partNum; string part; float price; string file = "parts.dat"; fstream inFile; inFile.open(file.c_str(), ios::in);

cout << "\nPart Number" << setw(12) << "Price" << setw(18) << "Description\n\n"; inFile >> partNum >> part >> price; while (!inFile.eof()) { cout << setw(8) << partNum << setw(8) << '$' << setw(8) << price << setw(5) << " " << part << endl; inFile >> partNum >> part >> price; } inFile.close(); return 0;}

File existence

• fail()

string file;cout << "Please enter a file name: ";getline(cin, file);fstream inFile;inFile.open(file.c_str(), ios::in);

if (inFile.fail()){ cout << "Sorry, I can't find the file\n"; exit(1);}

Example code:

Located in:

/class-files/samples/strings/

stringpractice.cpp

stringinput.cpp

stringoperations.cpp

Located in:

/class-files/samples/files

ask.cpp

infile.cpp

mixed.cpp

int.dat

parts.dat