Difference between string and char types in C

Question

I know a little C and now I m taking a look at C    I m used to char arrays for dealing with C strings  but while I look at C   code I see there are examples using both string type and char arrays    include  lt iostream gt   include  lt string gt  using namespace std   int main        string mystr    cout  lt  lt   What s your name       getline  cin  mystr     cout  lt  lt   Hello    lt  lt  mystr  lt  lt     n     cout  lt  lt   What is your favorite team       getline  cin  mystr     cout  lt  lt   I like    lt  lt  mystr  lt  lt    too  n     return 0      and   include  lt iostream gt  using namespace std   int main        char name 256   title 256      cout  lt  lt   Enter your name       cin getline  name 256      cout  lt  lt   Enter your favourite movie       cin getline  title 256      cout  lt  lt  name  lt  lt    s favourite movie is    lt  lt  title     return 0       both examples from http   www cplusplus com   I suppose this is a widely asked and answered  obvious   question  but it would be nice if someone could tell me what s exactly the difference between that two ways for dealing with strings in C    performance  API integration  the way each one is better         Thank you

User · Answer

I personally do not see any reason why one would like to use char* or char[] except for compatibility with old code. std::string's no slower than using a c-string, except that it will handle re-allocation for you. You can set it's size when you create it, and thus avoid re-allocation if you want. It's indexing operator ([]) provides constant time access (and is in every sense of the word the exact same thing as using a c-string indexer). Using the at method gives you bounds checked safety as well, something you don't get with c-strings, unless you write it. Your compiler will most often optimize out the indexer use in release mode. It is easy to mess around with c-strings; things such as delete vs delete[], exception safety, even how to reallocate a c-string.

And when you have to deal with advanced concepts like having COW strings, and non-COW for MT etc, you will need std::string.

If you are worried about copies, as long as you use references, and const references wherever you can, you will not have any overhead due to copies, and it's the same thing as you would be doing with the c-string.

User · Answer

Arkaitz is correct that string is a managed type   What this means for you is that you never have to worry about how long the string is  nor do you have to worry about freeing or reallocating the memory of the string   On the other hand  the char   notation in the case above has restricted the character buffer to exactly 256 characters   If you tried to write more than 256 characters into that buffer  at best you will overwrite other memory that your program  owns    At worst  you will try to overwrite memory that you do not own  and your OS will kill your program on the spot   Bottom line   Strings are a lot more programmer friendly  char  s are a lot more efficient for the computer

User · Answer

A char array is just that - an array of characters    If allocated on the stack  like in your example   it will always occupy eg  256 bytes no matter how long the text it contains is If allocated on the heap  using malloc   or new char    you re responsible for releasing the memory afterwards and you will always have the overhead of a heap allocation   If you copy a text of more than 256 chars into the array  it might crash  produce ugly assertion messages or cause unexplainable  mis- behavior somewhere else in your program  To determine the text s length  the array has to be scanned  character by character  for a  0 character    A string is a class that contains a char array  but automatically manages it for you  Most string implementations have a built-in array of 16 characters  so short strings don t fragment the heap  and use the heap for longer strings   You can access a string s char array like this   std  string myString    Hello World   const char  myStringChars   myString c str      C   strings can contain embedded  0 characters  know their length without counting  are faster than heap-allocated char arrays for short texts and protect you from buffer overruns  Plus they re more readable and easier to use     However  C   strings are not  very  suitable for usage across DLL boundaries  because this would require any user of such a DLL function to make sure he s using the exact same compiler and C   runtime implementation  lest he risk his string class behaving differently   Normally  a string class would also release its heap memory on the calling heap  so it will only be able to free memory again if you re using a shared   dll or  so  version of the runtime   In short  use C   strings in all your internal functions and methods  If you ever write a  dll or  so  use C strings in your public  dll so-exposed  functions

User · Answer

One of the difference is Null termination   0    In C and C    char  or char   will take a pointer to a single char as a parameter and will track along the memory until a 0 memory value is reached  often called the null terminator    C   strings can contain embedded  0 characters  know their length without counting     include lt stdio h gt   include lt string h gt   include lt iostream gt   using namespace std   void NullTerminatedString string str      int NUll term   3     str NUll term      0            specific character is kept as NULL in string    cout  lt  lt  str  lt  lt  endl  lt  lt endl  lt  lt endl     void NullTerminatedChar char  str      int NUll term   3     str NUll term    0         from specific  all the character are removed     cout  lt  lt  str  lt  lt  endl     int main      string str    Feels Happy     printf  string    s n   str c str       printf  strlen    d n   strlen str c str          printf  size    d n   str size         printf  sizeof    d n   sizeof str       sizeof std  string class  and compiler dependent   NullTerminatedString str       char str1 12     Feels Happy     printf  char      s n   str1     printf  strlen    d n   strlen str1      printf  sizeof    d n   sizeof str1          sizeof char array   NullTerminatedChar str1     return 0      Output   strlen   11 size   11 sizeof   32   Fee s Happy   strlen   11 sizeof   12 Fee

User · Answer

Think of  char    as string begin    The essential difference is that  char    is an iterator and std  string is a container  If you stick to basic strings a  char    will give you what std  string  iterator does  You could use  char    when you want the benefit of an iterator and also compatibility with C  but that s the exception and not the rule  As always  be careful of iterator invalidation  When people say  char    isn t safe this is what they mean  It s as safe as any other C   iterator

User · Answer

Strings have helper functions and manage char arrays automatically  You can concatenate strings  for a char array you would need to copy it to a new array  strings can change their length at runtime  A char array is harder to manage than a string and certain functions may only accept a string as input  requiring you to convert the array to a string  It s better to use strings  they were made so that you don t have to use arrays  If arrays were objectively better we wouldn t have strings

User · Answer

Well  string type is a completely managed class for character strings  while char   is still what it was in C  a byte array representing a character string for you   In terms of API and standard library everything is implemented in terms of strings and not char    but there are still lots of functions from the libc that receive char   so you may need to use it for those  apart from that I would always use std  string   In terms of efficiency of course a raw buffer of unmanaged memory will almost always be faster for lots of things  but take in account comparing strings for example  std  string has always the size to check it first  while with char   you need to compare character by character

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