What is use of c str function In c

Question

I have just started reading C   and found c   having rich functions for string manipulation which C does not have  I am reading these function and came across c str   and from what I understand is c str convert a string which may be null terminated or may not be to a null terminated string  Is it true   Can anyone suggest me some example so that i can understand the use of c str function

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Most OLD c   and c functions  when deal with strings  use const char   With STL and std  string  string c str   is introduced to be able to convert from std  string to const char    That means that if you promise not to change the buffer  you ll be able to use read only string contents   PROMISE   const char

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In C C   programming there are two types of strings  the C strings and the standard strings  With the  lt string gt  header  we can use the standard strings  On the other hand  the C strings are just an array of normal chars  So  in order to convert a standard string to a C string  we use the c str   function   for example     a string to a C-style string conversion    const char  cstr1   str1 c str    cout lt  lt  Operation   cstr1   str1 c str    lt  lt endl  cout lt  lt  The C-style string c str1 is    lt  lt cstr1 lt  lt endl  cout lt  lt   nOperation  strlen cstr1   lt  lt endl  cout lt  lt  The length of C-style string str1     lt  lt strlen cstr1  lt  lt endl    And the output will be   Operation   cstr1   str1 c str   The C-style string c str1 is  Testing the c str  Operation  strlen cstr1  The length of C-style string str1   17

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c str   converts a C   string into a C-style string which is essentially a null terminated array of bytes  You use it when you want to pass a C   string into a function that expects a C-style string  e g  a lot of the Win32 API  POSIX style functions  etc

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In C    you define your strings as  std  string MyString   instead of  char MyString 20     While writing C   code  you encounter some C functions which require C string as parameter  Like below   void IAmACFunction int abc  float bcd  const char   cstring    Now there is a problem  You are working with C   and you are using std  string string variables  But this C function is asking for a C string  How do you convert your std  string to a standard C string   Like this   std  string MyString         MyString    Hello world           IAmACFunction 5  2 45f  MyString c str       This is what c str   is for   Note that  for std  wstring strings  c str   returns a const w char

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c str returns a const char  that points to a null-terminated string  i e  a C-style string   It is useful when you want to pass the  contents    of an std  string to a function that expects to work with a C-style string   For example  consider this code   std  string str  Hello world     int pos1   str find first of  w     int pos2   strchr str c str     w   - str c str     if  pos1    pos2        printf  Both ways give the same result  n        See it in action   Notes      This is not entirely true because an std  string  unlike a C string  can contain the  0 character  If it does  the code that receives the return value of c str   will be fooled into thinking that the string is shorter than it really is  since it will interpret  0 as the end of the string

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Oh must add my own pick here  you will use this when you encode decode some string obj you transfer between two programs   Lets say you use base64encode some array in python  and then you want to decode that into c    Once you have the string you decode from base64decode in c    In order to get it back to array of float  all you need to do here is    float arr 1024   memcpy arr  ur string c str    sizeof float    1024     This is pretty common use I suppose

User · Answer

It s used to make std  string interoperable with C code that requires a null terminated char

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