char* vs std:string vs char[] in C++
In this article, we are going to inspect three different ways of initializing strings in C++ and discuss differences between them.
1. Using char*
Here, str is basically a pointer to the (const)string literal.
Syntax:
char* str = "This is GeeksForGeeks";
Pros:
1. Only one pointer is required to refer to whole string. That shows this is memory efficient.
2. No need to declare the size of string beforehand.
CPP
#include <iostream>
using namespace std;
int main()
{
char * str = "Hello" ;
const char * str1 = "Hello" ;
str[1] = 'o' ;
cout << str << endl;
return 0;
}
|
Output:
This is GeeksForGeeks
GeeksForGeeks For Everyone
Cons:
1. This works fine in C but writing in this form is a bad idea in C++. That’s why compiler shows warning of “deprecated conversion from string constant to ‘char*'” because in C string literals are arrays of char but in C++ they are constant array of char. Therefore use const keyword before char*.
const char* str = "This is GeeksForGeeks";
2. We cannot modify the string at later stage in program. We can change str to point something else but cannot change value present at str. Refer storage-for-strings-in-c for more detail.
CPP
#include <iostream>
using namespace std;
int main()
{
string s1 = "Hello" ;
string s2 = "World" ;
cout << s1.size() << endl;
cout << s2.length() << endl;
s1 = s1 + s2;
cout << s1 << endl;
s1.append( "Geeks" );
cout << s1 << endl;
string s3 = "HelloWorldGeeks" ;
if (s1.compare(s3) == 0)
cout << "true" << endl;
else
cout << "false" << endl;
string sub = s1.substr(0, 5);
cout << sub << endl;
s1.insert(10, "For" );
cout << s1 << endl;
string target = "World" ;
size_t pos = s1.find(target);
if (pos != std::string::npos)
cout << "Found at Position:" << pos << endl;
cout << s1.replace(5, 5, "Geeks" ) << endl;
return 0;
}
|
Output:
Segmentation Fault
2. Using std::string
Syntax:
std::string str = "This is GeeksForGeeks";
Here str is the object of std::string class which is an instantiation of the basic_string class template that uses char (i.e., bytes) as its character type.
Note: Do not use cstring or string.h functions when you are declaring string with std::string keyword because std::string strings are of basic_string class type and cstring strings are of const char* type. Pros: When dealing exclusively in C++ std:string is the best way to go because of better searching, replacement, and manipulation functions. Some of the useful std:string functions are discussed below.
CPP
#include <iostream>
using namespace std;
int main()
{
char str[] = "Hello" ;
str[1] = 'o' ;
cout << str << endl;
return 0;
}
|
Output:
5
5
HelloWorld
HelloWorldGeeks
true
Hello
HelloWorldForGeeks
Found at Position:5
HelloGeeksForGeeks
Cases where you might prefer char* over std:string
1. When dealing with lower level access like talking to the OS, but usually, if you’re passing the string to the OS then std::string::c_str has it covered.
2. Compatibility with old C code (although std::string’s c_str() method handles most of this).
3. To conserve memory (std::string will likely have more overhead).
3. Using char[]
Syntax:
char str[] = "This is GeeksForGeeks";
or
char str[size] = "This is GeeksForGeeks";
// Here str is a array of characters denoting the string.
Pros:
1. We can modify the string at later stage in program.
CPP
#include <iostream>
#include <cstring>
using namespace std;
int main()
{
char str[10] = "Hello" ;
cout << "Before Concatenation : " << str << endl;
strcat (str, " World" );
cout << "After Concatenation : " << str;
return 0;
}
|
Output:
Hollo
Cons:
1. This is statically allocated sized array which consumes space in the stack.
2. We need to take the large size of array if we want to concatenate or manipulate with other strings since the size of string is fixed. We can use C++ standard library cstring or string.h for that purpose.
CPP
#include
#include
using namespace std;
int main()
{
char s1[10] = “Hello”;
// return length of s1
cout << strlen(s1) << endl;
char s2[50];
// copies s1 into s2
strcpy(s2, s1);
cout << s2 << endl;
char s3[10] = "World";
// concatenates s3 into s2
strcat(s2, s3);
cout << s2 << endl;
char s4[50] = "HelloWorld";
// return 0 if s2 and s4 are equal.
if (strcmp(s2, s4) == 0)
cout << "true" << endl;
else
cout << "false" << endl;
char s5[30];
// copies first 5 chars of s4 into s5
strncpy(s5, s4, 5);
cout << s5 << endl;
char target[10] = "Hello";
// search for target string in s4
if (strstr(s4, target) != NULL)
cout << "true" << endl;
else
cout << "false" << endl;
return 0;
}
Output:
Before Concatenation : Hello
After Concatenation : Hello World
Here are couple of other useful functions of C++ standard library cstring.
Output :
5
Hello
HelloWorld
true
Hello
true
Last Updated :
15 Nov, 2023
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