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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<title>C++ Strings</title>
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<div class="header-box">
<a href="../index-2.html">cppreference.com</a> > <a href=
"index.html">C++ Strings</a>
</div>
<div class="name-format">
append
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <string>
string& append( const string& str );
string& append( const char* str );
string& append( const string& str, <strong>size_type</strong> index, <strong>size_type</strong> len );
string& append( const char* str, <strong>size_type</strong> num );
string& append( <strong>size_type</strong> num, char ch );
string& append( <a href=
"../iterators.html">input_iterator</a> start, <a href=
"../iterators.html">input_iterator</a> end );
</pre>
<p>The append() function either:</p>
<ul>
<li>appends <em>str</em> on to the end of the current string,</li>
<li>appends a substring of <em>str</em> starting at <em>index</em>
that is <em>len</em> characters long on to the end of the current
string,</li>
<li>appends <em>num</em> characters of <em>str</em> on to the end
of the current string,</li>
<li>appends <em>num</em> repititions of <em>ch</em> on to the end
of the current string,</li>
<li>or appends the sequence denoted by <em>start</em> and
<em>end</em> on to the end of the current string.</li>
</ul>
<p>For example, the following code uses append() to add 10 copies of
the '!' character to a string:</p>
<pre class="prettyprint">
string str = "Hello World";
str.append( 10, '!' );
cout << str << endl;
</pre>
<p>That code displays:</p>
<pre class="prettyprint">
Hello World!!!!!!!!!!
</pre>
<p>In the next example, append() is used to concatenate a substring
of one string onto another string:</p>
<pre class="prettyprint">
string str1 = "Eventually I stopped caring...";
string str2 = "but that was the '80s so nobody noticed.";
str1.append( str2, 25, 15 );
cout << "str1 is " << str1 << endl;
</pre>
<p>When run, the above code displays:</p>
<pre class="prettyprint">
str1 is Eventually I stopped caring...nobody noticed.
</pre>
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<div class="name-format">
assign
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <string>
void assign( <strong>size_type</strong> num, const char& val );
void assign( <a href=
"../iterators.html">input_iterator</a> start, <a href=
"../iterators.html">input_iterator</a> end );
string& assign( const string& str );
string& assign( const char* str );
string& assign( const char* str, <strong>size_type</strong> num );
string& assign( const string& str, <strong>size_type</strong> index, <strong>size_type</strong> len );
string& assign( <strong>size_type</strong> num, const char& ch );
</pre>
<p>The default assign() function gives the current string the values
from <em>start</em> to <em>end</em>, or gives it <em>num</em> copies
of <em>val</em>.</p>
<p>In addition to the normal (C++ Lists) <a href=
"../cpplist/assign.html">assign</a>() functionality that all C++
containers have, strings possess an assign() function that also
allows them to:</p>
<ul>
<li>assign <em>str</em> to the current string,</li>
<li>assign the first <em>num</em> characters of <em>str</em> to the
current string,</li>
<li>assign a substring of <em>str</em> starting at <em>index</em>
that is <em>len</em> characters long to the current string,</li>
</ul>
<p>For example, the following code:</p>
<pre class="prettyprint">
string str1, str2 = "War and Peace";
str1.assign( str2, 4, 3 );
cout << str1 << endl;
</pre>
<p>displays</p>
<pre class="prettyprint">
and
</pre>
<p>This function will destroy the previous contents of the
string.</p>
<div class="related-name-format">
Related topics:
</div>
<div class="related-content">
(C++ Lists) <a href="../cpplist/assign.html">assign</a>
</div>
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<hr>
<div class="name-format">
at
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <string>
<a href=
"../containers.html">TYPE</a>& at( <strong>size_type</strong> loc );
const <a href=
"../containers.html">TYPE</a>& at( <strong>size_type</strong> loc ) const;
</pre>
<p>The at() function returns a reference to the element in the string
at index <em>loc</em>. The at() function is safer than the []
operator, because it won't let you reference items outside the
bounds of the string.</p>
<p>For example, consider the following code:</p>
<pre class="prettyprint">
vector<int> v( 5, 1 );
for( int i = 0; i < 10; i++ ) {
cout << "Element " << i << " is " << v[i] << endl;
}
</pre>
<p>This code overrunns the end of the vector, producing potentially
dangerous results. The following code would be much safer:</p>
<pre class="prettyprint">
vector<int> v( 5, 1 );
for( int i = 0; i < 10; i++ ) {
cout << "Element " << i << " is " << v.at(i) << endl;
}
</pre>
<p>Instead of attempting to read garbage values from memory, the at()
function will realize that it is about to overrun the vector and will
throw an exception.</p>
<div class="related-name-format">
Related topics:
</div>
<div class="related-content">
(C++ Multimaps) <a href=
"../cppmultimap/multimap_operators.html">Multimap
operators</a><br>
(C++ Double-ended Queues) <a href=
"../cppdeque/container_operators.html">Container operators</a>
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<hr>
<div class="name-format">
begin
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <string>
iterator begin();
const_iterator begin() const;
</pre>
<p>The function begin() returns an iterator to the first element of
the string. begin() should run in <a href=
"../complexity.html">constant time</a>.</p>
<p>For example, the following code uses begin() to initialize an
iterator that is used to traverse a list:</p>
<pre class="prettyprint">
// Create a list of characters
list<char> charList;
for( int i=0; i < 10; i++ ) {
charList.push_front( i + 65 );
}
// Display the list
list<char>::iterator theIterator;
for( theIterator = charList.begin(); theIterator != charList.end(); theIterator++ ) {
cout << *theIterator;
}
</pre>
<div class="related-name-format">
Related topics:
</div>
<div class="related-content">
<a href="end.html">end</a><br>
<a href="rbegin.html">rbegin</a><br>
<a href="rend.html">rend</a>
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<hr>
<div class="name-format">
c_str
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <string>
const char* c_str();
</pre>
<p>The function c_str() returns a const pointer to a regular C
string, identical to the current string. The returned string is
null-terminated.</p>
<p>Note that since the returned pointer is of type <a
href="../keywords/const.html">const</a>, the character data that
c_str() returns <strong>cannot be modified</strong>. Furthermore,
you do not need to call <a
href="http://www.cppreference.com/stdmem/free.html">free()</a> or <a
href="http://www.cppreference.com/keywords/delete.html">delete</a>
on this pointer.</p>
<div class="related-name-format">
Related topics:
</div>
<div class="related-content">
<a href="string_operators.html">String operators</a><br>
<a href="data.html">data</a>
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<hr>
<div class="name-format">
capacity
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <string>
<strong>size_type</strong> capacity() const;
</pre>
<p>The capacity() function returns the number of elements that the
string can hold before it will need to allocate more space.</p>
<p>For example, the following code uses two different methods to set
the capacity of two vectors. One method passes an argument to the
constructor that suggests an initial size, the other method calls the
reserve function to achieve a similar goal:</p>
<pre class="prettyprint">
vector<int> v1(10);
cout << "The capacity of v1 is " << v1.capacity() << endl;
vector<int> v2;
v2.reserve(20);
cout << "The capacity of v2 is " << v2.capacity() << endl;
</pre>
<p>When run, the above code produces the following output:</p>
<pre class="prettyprint">
The capacity of v1 is 10
The capacity of v2 is 20
</pre>
<p>C++ containers are designed to grow in size dynamically. This
frees the programmer from having to worry about storing an arbitrary
number of elements in a container. However, sometimes the programmer
can improve the performance of her program by giving hints to the
compiler about the size of the containers that the program will use.
These hints come in the form of the <a href=
"reserve.html">reserve</a>() function and the constructor used in the
above example, which tell the compiler how large the container is
expected to get.</p>
<p>The capacity() function runs in <a href=
"../complexity.html">constant time</a>.</p>
<div class="related-name-format">
Related topics:
</div>
<div class="related-content">
<a href="reserve.html">reserve</a><br>
<a href="resize.html">resize</a><br>
<a href="size.html">size</a>
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<div class="name-format">
clear
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <string>
void clear();
</pre>
<p>The function clear() deletes all of the elements in the string.
clear() runs in <a href="../complexity.html">linear time</a>.</p>
<div class="related-name-format">
Related topics:
</div>
<div class="related-content">
(C++ Lists) <a href="../cpplist/erase.html">erase</a>
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<div class="name-format">
compare
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <string>
int compare( const string& str );
int compare( const char* str );
int compare( <strong>size_type</strong> index, <strong>size_type</strong> length, const string& str );
int compare( <strong>size_type</strong> index, <strong>size_type</strong> length, const string& str, <strong>size_type</strong> index2,
<strong>size_type</strong> length2 );
int compare( <strong>size_type</strong> index, <strong>size_type</strong> length, const char* str, <strong>size_type</strong> length2 );
</pre>
<p>The compare() function either compares <em>str</em> to the current
string in a variety of ways, returning</p>
<table class="code-table">
<tr>
<th class="code-table-th">Return Value</th>
<th class="code-table-th">Case</th>
</tr>
<tr>
<td class="code-table-td">less than zero</td>
<td class="code-table-td">this < str</td>
</tr>
<tr>
<td class="code-table-td">zero</td>
<td class="code-table-td">this == str</td>
</tr>
<tr>
<td class="code-table-td">greater than zero</td>
<td class="code-table-td">this > str</td>
</tr>
</table>
<p>The various functions either:</p>
<ul>
<li>compare <em>str</em> to the current string,</li>
<li>compare <em>str</em> to a substring of the current string,
starting at <em>index</em> for <em>length</em> characters,</li>
<li>compare a substring of <em>str</em> to a substring of the
current string, where <em>index2</em> and <em>length2</em> refer to
<em>str</em> and <em>index</em> and <em>length</em> refer to the
current string,</li>
<li>or compare a substring of <em>str</em> to a substring of the
current string, where the substring of <em>str</em> begins at zero
and is <em>length2</em> characters long, and the substring of the
current string begins at <em>index</em> and is <em>length</em>
characters long.</li>
</ul>
<p>For example, the following code uses compare() to compare four
strings with eachother:</p>
<pre class="prettyprint">
string names[] = {"Homer", "Marge", "3-eyed fish", "inanimate carbon rod"};
for( int i = 0; i < 4; i++ ) {
for( int j = 0; j < 4; j++ ) {
cout << names[i].compare( names[j] ) << " ";
}
cout << endl;
}
</pre>
<p>Data from the above code was used to generate this table, which
shows how the various strings compare to eachother:</p>
<table class="code-table">
<tr>
<th class="code-table-th"></th>
<th class="code-table-th">Homer</th>
<th class="code-table-th">Marge</th>
<th class="code-table-th">3-eyed fish</th>
<th class="code-table-th">inanimate carbon rod</th>
</tr>
<tr>
<td class="code-table-td">"Homer".compare( x )</td>
<td class="code-table-td">0</td>
<td class="code-table-td">-1</td>
<td class="code-table-td">1</td>
<td class="code-table-td">-1</td>
</tr>
<tr>
<td class="code-table-td">"Marge".compare( x )</td>
<td class="code-table-td">1</td>
<td class="code-table-td">0</td>
<td class="code-table-td">1</td>
<td class="code-table-td">-1</td>
</tr>
<tr>
<td class="code-table-td">"3-eyed fish".compare( x
)</td>
<td class="code-table-td">-1</td>
<td class="code-table-td">-1</td>
<td class="code-table-td">0</td>
<td class="code-table-td">-1</td>
</tr>
<tr>
<td class="code-table-td">"inanimate carbon
rod".compare( x )</td>
<td class="code-table-td">1</td>
<td class="code-table-td">1</td>
<td class="code-table-td">1</td>
<td class="code-table-td">0</td>
</tr>
</table>
<div class="related-name-format">
Related topics:
</div>
<div class="related-content">
<a href="string_operators.html">String operators</a>
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<hr>
<div class="name-format">
copy
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <string>
<strong>size_type</strong> copy( char* str, <strong>size_type</strong> num, <strong>size_type</strong> index = 0 );
</pre>
<p>The copy() function copies <em>num</em> characters of the current
string (starting at <em>index</em> if it's specified, 0
otherwise) into <em>str</em>.</p>
<p>The return value of copy() is the number of characters copied.</p>
<p>For example, the following code uses copy() to extract a substring
of a string into an array of characters:</p>
<pre class="prettyprint">
char buf[30];
memset( buf, '\0', 30 );
string str = "Trying is the first step towards failure.";
str.copy( buf, 24 );
cout << buf << endl;
</pre>
<p>When run, this code displays:</p>
<pre class="prettyprint">
Trying is the first step
</pre>
<p>Note that before calling copy(), we first call (Standard C String
and Character) <a href="../stdstring/memset.html">memset</a>() to
fill the destination array with copies of the <strong>NULL</strong>
character. This step is included to make sure that the resulting
array of characters is <strong>NULL</strong>-terminated.</p>
<div class="related-name-format">
Related topics:
</div>
<div class="related-content">
<a href="substr.html">substr</a>
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<hr>
<div class="name-format">
data
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <string>
const char *data();
</pre>
<p>The function data() returns a pointer to the first character in
the current string.</p>
<div class="related-name-format">
Related topics:
</div>
<div class="related-content">
<a href="string_operators.html">String operators</a><br>
<a href="c_str.html">c_str</a>
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<hr>
<div class="name-format">
empty
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <string>
bool empty() const;
</pre>
<p>The empty() function returns true if the string has no elements,
false otherwise.</p>
<p>For example:</p>
<pre class="prettyprint">
string s1;
string s2("");
string s3("This is a string");
cout.setf(ios::boolalpha);
cout << s1.empty() << endl;
cout << s2.empty() << endl;
cout << s3.empty() << endl;
</pre>
<p>When run, this code produces the following output:</p>
<pre class="example-output">
true
true
false
</pre>
<div class="related-name-format">
Related topics:
</div>
<div class="related-content">
<a href="size.html">size</a>
</div>
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<hr>
<div class="name-format">
end
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <string>
iterator end();
const_iterator end() const;
</pre>
<p>The end() function returns an iterator just past the end of the
string.</p>
<p>Note that before you can access the last element of the string
using an iterator that you get from a call to end(), you'll have
to decrement the iterator first.</p>
<p>For example, the following code uses <a href=
"begin.html">begin</a>() and end() to iterate through all of the
members of a vector:</p>
<pre class="prettyprint">
vector<int> v1( 5, 789 );
vector<int>::iterator it;
for( it = v1.begin(); it != v1.end(); it++ ) {
cout << *it << endl;
}
</pre>
<p>The iterator is initialized with a call to <a href=
"begin.html">begin</a>(). After the body of the loop has been
executed, the iterator is incremented and tested to see if it is
equal to the result of calling end(). Since end() returns an iterator
pointing to an element just after the last element of the vector, the
loop will only stop once all of the elements of the vector have been
displayed.</p>
<p>end() runs in <a href="../complexity.html">constant time</a>.</p>
<div class="related-name-format">
Related topics:
</div>
<div class="related-content">
<a href="begin.html">begin</a><br>
<a href="rbegin.html">rbegin</a><br>
<a href="rend.html">rend</a>
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<div class="name-format">
erase
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <string>
iterator erase( iterator loc );
iterator erase( iterator start, iterator end );
string& erase( <strong>size_type</strong> index = 0, <strong>size_type</strong> num = npos );
</pre>
<p>The erase() function either:</p>
<ul>
<li>removes the character pointed to by <em>loc</em>, returning an
iterator to the next character,</li>
<li>removes the characters between <em>start</em> and <em>end</em>
(including the one at <em>start</em> but not the one at
<em>end</em>), returning an iterator to the character after the
last character removed,</li>
<li>or removes <em>num</em> characters from the current string,
starting at <em>index</em>, and returns *this.</li>
</ul>
<p>The parameters <em>index</em> and <em>num</em> have default
values, which means that erase() can be called with just
<em>index</em> to erase all characters after <em>index</em> or with
no arguments to erase all characters.</p>
<p>For example:</p>
<pre class="prettyprint">
string s("So, you like donuts, eh? Well, have all the donuts in the world!");
cout << "The original string is '" << s << "'" << endl;
s.erase( 50, 14 );
cout << "Now the string is '" << s << "'" << endl;
s.erase( 24 );
cout << "Now the string is '" << s << "'" << endl;
s.erase();
cout << "Now the string is '" << s << "'" << endl;
</pre>
<p>will display</p>
<pre class="prettyprint">
The original string is 'So, you like donuts, eh? Well, have all the donuts in the world!'
Now the string is 'So, you like donuts, eh? Well, have all the donuts'
Now the string is 'So, you like donuts, eh?'
Now the string is ''
</pre>
<p>erase() runs in <a href="../complexity.html">linear time</a>.</p>
<div class="related-name-format">
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</div>
<div class="related-content">
<a href="insert.html">insert</a>
</div>
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<div class="name-format">
find
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <string>
<strong>size_type</strong> find( const string& str, <strong>size_type</strong> index );
<strong>size_type</strong> find( const char* str, <strong>size_type</strong> index );
<strong>size_type</strong> find( const char* str, <strong>size_type</strong> index, <strong>size_type</strong> length );
<strong>size_type</strong> find( char ch, <strong>size_type</strong> index );
</pre>
<p>The function find() either:</p>
<ul>
<li>returns the first occurrence of <em>str</em> within the current
string, starting at <em>index</em>, string::npos if nothing is
found,</li>
<li>if the <em>length</em> parameter is given, then find() returns
the first occurrence of the first <em>length</em> characters of
<em>str</em> within the current string, starting at
<em>index</em>, string::npos if nothing is found,</li>
<li>or returns the index of the first occurrence <em>ch</em> within
the current string, starting at <em>index</em>, string::npos if
nothing is found.</li>
</ul>
<p>For example:</p>
<pre class="prettyprint">
string str1( "Alpha Beta Gamma Delta" );