The STL string Class
The STL string class std::string helps you in the following ways:
- Reduces the effort of creation and manipulating strings
- Increases the stability of the application being programmed by internally managing memory allocation details
- Supplies copy constructor and assignment operators that automatically ensure that member strings get correctly copied
- Supplies useful utility functions that help in copying, truncating, finding, and erasing to name a few
- Provides operators that help in comparisons
- Focuses efforts on your application's primary requirements rather than on string manipulation details
The most commonly used string functions are
- Copying
- Concatenating
- Finding characters and substrings
- Truncating
- String reversal and case conversion are achieved using algorithms provided by the standard library
#include <string>
#include <iostream>
int main ()
{
using namespace std;
const char* pszConstString = "Hello String!";
cout << "Constant string is: " << pszConstString << endl;
std::string strFromConst (pszConstString);
cout << "strFromConst is: " << strFromConst << endl;
std::string str2 ("Hello String!");
std::string str2Copy (str2);
cout << "str2Copy is: " << str2Copy << endl;
// Initialize a string to the first 5 characters of another
std::string strPartialCopy (pszConstString, 5);
cout << "strPartialCopy is: " << strPartialCopy << endl;
// Initialize a string object to contain 10 'a's
std::string strRepeatChars (10, 'a');
cout << "strRepeatChars is: " << strRepeatChars << endl;
return 0;
}
Output:
Constant string is: Hello String!
strFromConst is: Hello String!
str2Copy is: Hello String!
strPartialCopy is: Hello
strRepeatChars is: aaaaaaaaaa
Accessing a string and Its Contents
#include <string>
#include <iostream>
int main ()
{
using namespace std;
// The sample string
string strSTLString ("Hello String");
// Access the contents of the string using array syntax
cout << "Displaying characters using array-syntax: " << endl;
for ( size_t nCharCounter = 0
; nCharCounter < strSTLString.length ()
; ++ nCharCounter )
{
cout << "Character [" << nCharCounter << "] is: ";
cout << strSTLString [nCharCounter] << endl;
}
cout << endl;
// Access the contents of a string using iterators
cout << "Displaying characters using iterators: " << endl;
int nCharOffset = 0;
string::const_iterator iCharacterLocator;
for ( iCharacterLocator = strSTLString.begin ()
; iCharacterLocator != strSTLString.end ()
; ++ iCharacterLocator )
{
cout << "Character [" << nCharOffset ++ << "] is: ";
cout << *iCharacterLocator << endl;
}
cout << endl;
// Access the contents of a string as a C-style string
cout << "The char* representation of the string is: ";
cout << strSTLString.c_str () << endl;
return 0;
}
Output:
Displaying the elements in the string using array-syntax:
Character [0] is: H
Character [1] is: e
Character [2] is: l
Character [3] is: l
Character [4] is: o
Character [5] is:
Character [6] is: S
Character [7] is: t
Character [8] is: r
Character [9] is: i
Character [10] is: n
Character [11] is: g
Displaying the contents of the string using iterators:
Character [0] is: H
Character [1] is: e
Character [2] is: l
Character [3] is: l
Character [4] is: o
Character [5] is:
Character [6] is: S
Character [7] is: t
Character [8] is: r
Character [9] is: i
Character [10] is: n
Character [11] is: g
String Concatenation
#include <string>
#include <iostream>
int main ()
{
using namespace std;
string strSample1 ("Hello");
string strSample2 (" String!");
// Concatenate
strSample1 += strSample2;
cout << strSample1 << endl << endl;
string strSample3 (" Fun is not needing to use pointers!");
strSample1.append (strSample3);
cout << strSample1 << endl << endl;
const char* pszConstString = "You however still can!";
strSample1.append (pszConstString);
cout << strSample1 << endl;
return 0;
}
Output:
Hello String!
Hello String! Fun is not needing to use pointers!
Hello String! Fun is not needing to use pointers when working with strings. You
however still can!
Finding a Character or Substring in a string
#include <string>
#include <iostream>
int main ()
{
using namespace std;
string strSample ("Good day String! Today is beautiful!");
cout << "The sample string is: " << endl;
cout << strSample << endl << endl;
// Find substring "day" in it...
size_t nOffset = strSample.find ("day", 0);
// Check if the substring was found...
if (nOffset != string::npos)
cout << "First instance of \"day\" was found at offset " << nOffset;
else
cout << "Substring not found." << endl;
cout << endl << endl;
cout << "Locating all instances of substring \"day\"" << endl;
size_t nSubstringOffset = strSample.find ("day", 0);
while (nSubstringOffset != string::npos)
{
cout << "\"day\" found at offset " << nSubstringOffset << endl;
// Make the 'find' function search the next character onwards
size_t nSearchOffset = nSubstringOffset + 1;
nSubstringOffset = strSample.find ("day", nSearchOffset);
}
cout << endl;
cout << "Locating all instances of character 'a'" << endl;
const char chCharToSearch = 'a';
size_t nCharacterOffset = strSample.find (chCharToSearch, 0);
while (nCharacterOffset != string::npos)
{
cout << "'" << chCharToSearch << "' found";
cout << " at position: " << nCharacterOffset << endl;
// Make the 'find' function search forward from the next character
size_t nCharSearchOffset = nCharacterOffset + 1;
nCharacterOffset = strSample.find(chCharToSearch,nCharSearchOffset);
}
return 0;
}
Output:
The sample string is:
Good day String! Today is beautiful!
First instance of “day” was found at offset 5
Locating all instances of substring “day”
“day” found at offset 5
“day” found at offset 19
Locating all instances of character ‘a’
‘a’ found at position: 6
‘a’ found at position: 20
‘a’ found at position: 28
Truncate a STL string
#include <string>
#include <algorithm>
#include <iostream>
int main ()
{
using namespace std;
string strSample ("Hello String! Wake up to a beautiful day!");
cout << "The original sample string is: " << endl;
cout << strSample << endl << endl;
// Delete characters from the string given position and count
cout << "Truncating the second sentence: " << endl;
strSample.erase (13, 28);
cout << strSample << endl << endl;
// Find a character 'S' in the string using STL find algorithm
string::iterator iCharS = find ( strSample.begin ()
, strSample.end (), 'S');
// If character found, 'erase' to deletes a character
cout << "Erasing character 'S' from the sample string:" << endl;
if (iCharS != strSample.end ())
strSample.erase (iCharS);
cout << strSample << endl << endl;
// Erase a range of characters using an overloaded version of erase()
cout << "Erasing a range between begin() and end(): " << endl;
strSample.erase (strSample.begin (), strSample.end ());
// Verify the length after the erase() operation above
if (strSample.length () == 0)
cout << "The string is empty" << endl;
return 0;
}
Output:
The original sample string is:
Hello String! Wake up to a beautiful day!
Truncating the second sentence:
Hello String!
Erasing character ‘S’ from the sample string:
Hello tring!
Erasing a range between begin() and end():
The string is empty
String Reversal
// Listing 17.6 - Reversing an STL String
#include <string>
#include <iostream>
#include <algorithm>
int main ()
{
using namespace std;
string strSample ("Hello String! We will reverse you!");
cout << "The original sample string is: " << endl;
cout << strSample << endl << endl;
reverse (strSample.begin (), strSample.end ());
cout << "After applying the std::reverse algorithm: " << endl;
cout << strSample;
return 0;
}
Output:
The original sample string is:
Hello String! We will reverse you!
After applying the std::reverse algorithm:
!uoy esrever lliw eW !gnirtS olleH
String Case Conversion
// Listing 17.7 - Performing Case Conversions on an STL String Using std::transform
#include <string>
#include <iostream>
#include <algorithm>
int main ()
{
using namespace std;
cout << "Please enter a string for case-convertion:" << endl;
cout << "> ";
string strInput;
getline (cin, strInput);
cout << endl;
transform (strInput.begin(),strInput.end(),strInput.begin(),toupper);
cout << "The string converted to upper case is: " << endl;
cout << strInput << endl << endl;
transform (strInput.begin(),strInput.end(),strInput.begin(),tolower);
cout << "The string converted to lower case is: " << endl;
cout << strInput << endl << endl;
return 0;
}
Output:
Please enter a string for case-conversion:
> ConverT thIS StrINg!
The string converted to upper case is:
CONVERT THIS STRING!
The string converted to lower case is:
convert this string!
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