std string to char

Question

I want to convert a std  string into a char  or char   data type   std  string str    string   char  chr   str    Results in     error  cannot convert    std  string    to    char             What methods are there available to do this

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Conversion in OOP style  converter hpp  class StringConverter       public  static char   strToChar std  string str        converter cpp  char   StringConverter  strToChar std  string str        return  char  str c str        usage  StringConverter  strToChar  converted string

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If you just want a C-style string representing the same content   char const  ca   str c str     If you want a C-style string with new contents  one way  given that you don t know the string size at compile-time  is dynamic allocation   char  ca   new char str size   1   std  copy str begin    str end    ca   ca str size        0     Don t forget to delete   it later  If you want a statically-allocated  limited-length array instead   size t const MAX   80     maximum number of chars char ca MAX        std  copy str begin     str size    gt   MAX   str begin     MAX   str end     ca      std  string doesn t implicitly convert to these types for the simple reason that needing to do this is usually a design smell  Make sure that you really need it   If you definitely need a char   the best way is probably   vector lt char gt  v str begin    str end     char  ca    amp v 0      pointer to start of vector

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This will also work  std  string s  std  cout lt  lt  Enter the String   std  getline std  cin  s   char  a new char s size   1   a s size    0  memcpy a s c str   s size     std  cout lt  lt a

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char  result   strcpy  char  malloc str length   1   str c str

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Assuming you just need a C-style string to pass as input   std  string str    string   const char  chr   str c str

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No body ever mentioned sprintf  std  string s  char   c  sprintf c   quot  s quot   s c str

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You can make it using iterator   std  string str    string   std  string  iterator p str begin    char  chr    amp   p     Good luck

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To obtain a const char   from an std  string use the c str   member function    std  string str    string   const char  chr   str c str      To obtain a non-const char   from an std  string you can use the data   member function which returns a non-const pointer since C  17    std  string str    string   char  chr   str data      For older versions of the language  you can use range construction to copy the string into a vector from which a non-const pointer can be obtained    std  string str    string   std  vector lt char gt  str copy str c str    str c str     str size     1   char  chr   str copy data      But beware that this won t let you modify the string contained in str  only the copy s data can be changed this way  Note that it s specially important in older versions of the language to use c str   here because back then std  string wasn t guaranteed to be null terminated until c str   was called

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To be strictly pedantic  you cannot  convert a std  string into a char  or char   data type     As the other answers have shown  you can copy the content of the std  string to a char array  or make a const char  to the content of the std  string so that you can access it in a  C style    If you re trying to change the content of the std  string  the std  string type has all of the methods to do anything you could possibly need to do to it    If you re trying to pass it to some function which takes a char   there s std  string  c str

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Here is one more robust version from Protocol Buffer  char  string as array string  str        return str- gt empty     NULL    amp  str- gt begin          test codes std  string mystr  you are here    char  pstr   string as array  amp mystr   cout  lt  lt  pstr  lt  lt  endl     you are here

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If I d need a mutable raw copy of a c   s string contents  then I d do this    std  string str    string   char  chr   strdup str c str       and later   free chr      So why don t I fiddle with std  vector or new   like anyone else  Because when I need a mutable C-style raw char  string  then because I want to call C code which changes the string and C code deallocates stuff with free   and allocates with malloc    strdup uses malloc   So if I pass my raw string to some function X written in C it might have a constraint on it s argument that it has to allocated on the heap  for example if the function might want to call realloc on the parameter   But it is highly unlikely that it would expect an argument allocated with  some user-redefined  new

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It won t automatically convert  thank god   You ll have to use the method c str   to get the C string version   std  string str    string   const char  cstr   str c str      Note that it returns a const char    you aren t allowed to change the C-style string returned by c str    If you want to process it you ll have to copy it first   std  string str    string   char  cstr   new char str length     1   strcpy cstr  str c str        do stuff delete    cstr    Or in modern C     std  vector lt char gt  cstr str c str    str c str     str size     1

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A safe version of orlp s char  answer using unique ptr   std  string str    string   auto cstr   std  make unique lt char   gt  str length     1   strcpy cstr get    str c str

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More details here  and here but you can use   string str    some string    char  cstr    amp str 0

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For completeness  sake  don t forget std  string  copy     std  string str    string   const size t MAX   80  char chrs MAX    str copy chrs  MAX     std  string  copy   doesn t NUL terminate  If you need to ensure a NUL terminator for use in C string functions   std  string str    string   const size t MAX   80  char chrs MAX    memset chrs    0   MAX   str copy chrs  MAX-1

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This would be better as a comment on bobobobo s answer  but I don t have the rep for that  It accomplishes the same thing but with better practices   Although the other answers are useful  if you ever need to convert std  string to char  explicitly without const  const cast is your friend    std  string str    string   char  chr   const cast lt char  gt  str c str       Note that this will not give you a copy of the data  it will give you a pointer to the string  Thus  if you modify an element of chr  you ll modify str

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This answer applies to C  98 only    Please  don t use a raw char    std  string str    string   std  vector lt char gt  chars str c str    str c str     str size     1u      use  amp chars 0  as a char

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Alternatively   you can use vectors to get a writable char  as demonstrated below     this handles memory manipulations and is more convenient string str  vector  lt char gt  writable  str begin     str end    writable  push back    0     char  cstring    amp writable 0    or  amp  writable begin        Goodluck

[c++] std::string to char*

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