How to get rid of deprecated conversion from string constant to char warnings in GCC

Question

So I m working on an exceedingly large codebase  and recently upgraded to gcc 4 3  which now triggers this warning      warning  deprecated conversion from string constant to    char       Obviously  the correct way to fix this is to find every declaration like  char  s    constant string     or function call like   void foo char  s   foo  constant string      and make them const char pointers   However  that would mean touching 564 files  minimum  which is not a task I wish to perform at this point in time   The problem right now is that I m running with -werror  so I need some way to stifle these warnings   How can I do that

User · Answer

While passing string constants to functions write it as  void setpart const char name      setpart  quot Hello quot     instead of const char name    you could also write const char   name It worked for me to remove this error   Warning  deprecated conversion from string constant to  char    -Wwrite-strings

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Do typecasting from constant string to char pointer i e   char  s    char     constant string

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The problem right now is that I m running with -Werror   This is your real problem  IMO  You can try some automated ways of moving from  char    to  const char    but I would put money on them not just working  You will have to have a human involved for at least some of the work  For the short term  just ignore the warning  but IMO leave it on  or it ll never get fixed  and just remove the -Werror

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Check out gcc s Diagnostic Pragma support  and the list of -W warning options  changed  new link to warning options    For gcc  you can use  pragma warning directives like explained here

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Replace  char  str    hello     with  char  str    char   hello     or if you are calling in function   foo  hello      replace this with  foo  char    hello

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Instead of   void foo char  s   foo  constant string      This works   void foo const char s     foo  constant string

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I believe passing -Wno-write-strings to gcc will suppress this warning

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You can also create a writable string from a string constant by calling strdup     For instance  this code generates a warning   putenv  DEBUG 1      However  the following code does not  it makes a copy of the string on the heap before passing it to putenv    putenv strdup  DEBUG 1       In this case  and perhaps in most others  turning off the warning is a bad idea -- it s there for a reason   The other alternative  making all strings writable by default  is potentially inefficient   Listen to what the compiler is telling you

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Why don t you use the -Wno-deprecated option to ignore deprecated warning messages

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Here is how to do it inline in a file  so you don t have to modify your Makefile      gets rid of annoying  deprecated conversion from string constant blah blah  warning  pragma GCC diagnostic ignored  -Wwrite-strings    You can then later      pragma GCC diagnostic pop

User · Answer

Why not just use type casting    char    test

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see this situation   typedef struct tagPyTypeObject       PyObject HEAD      char  name      PrintFun print      AddFun add      HashFun hash    PyTypeObject   PyTypeObject PyDict Type        PyObject HEAD INIT  amp PyType Type        dict       dict print      0      0      watch the name field  in gcc it compile without warning  but in g   it will  i don t know why

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In C    Replace   char  str    hello     with   std  string str   hello      And if you want to compare it   str compare  HALLO

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I had a similar problem  I solved it like this    include  lt string h gt   extern void foo char  m    int main            warning  deprecated conversion from string constant to    char           foo  Hello            no more warning     char msg      Hello       foo msg       Is this an appropriate way of solving this  I do not have access to foo to adapt it to accept const char   although that would be a better solution  because foo does not change m

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Test string is const string  So you can solve like this   char str      Test string     or   const char  str    Test string   printf str

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In C    use the const cast as like below  char  str   const cast lt char  gt   Test string

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If it s an active code base  you might still want to upgrade the code base  Of course  performing the changes manually isn t feasible but I believe that this problem could be solved once and for all by one single sed command  I haven t tried it  though  so take the following with a grain of salt   find   -exec sed -E -i  backup -n       -e  s char s    s   w   s     char const   1     g          This might not find all places  even not considering function calls  but it would alleviate the problem and make it possible to perform the few remaining changes manually

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I can t use the compiler switch  So I have turned this   char  setf   tigetstr  setf      to this   char  setf   tigetstr  char    setf

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just use -w option for g    example   g   -w -o simple o simple cpp -lpthread  Remember this doesn t avoid deprecation rather it prevents showing warning message on the terminal   Now if you really want to avoid deprecation use const keyword like this   const char  s  constant string

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PyTypeObject PyDict Type         PyTypeObject PyDict Type      PyObject HEAD INIT  amp PyType Type                         dict                        dict print                       0                       0       watch the name field  in gcc it compile without warning  but in g   it will  i don t know why   in gcc  Compiling C   -Wno-write-strings is active by default   in g    Compiling C    -Wwrite-strings is active by default  This is why there is a different behaviour  For us using macros of Boost python generates such warnings  So we use -Wno-write-strings when compiling C   since we always use -Werror

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I don t understand how to apply your solution        kalmanIsAGameChanger   Working with Arduino Sketch  I had a function causing my warnings           Original function  char StrContains char  str  char  sfind       To stop the warnings I added the const in front of the char  str and the char  sfind            Modified  char StrContains const char  str  const char  sfind        All warnings went away

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Thanks  all  for the help   Picking from here and there comes this solution   This compiles clean   Have not tested the code yet   Tomorrow     maybe     const char   timeServer        pool ntp org        0 - Worldwide   define WHICH NTP            0    Which NTP server name to use      sendNTPpacket const cast lt char  gt  timeServer WHICH NTP        send an NTP packet to a server     void sendNTPpacket char  address    code     I know  there s only 1 item in the timeServer array   But there could be more   The rest were commented out for now to save memory

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Any functions into which you pass string literals  I am a string literal  should use char const   as the type instead of char    If you re going to fix something  fix it right   Explanation   You can not use string literals to initialise strings that will be modified  because they are of type const char   Casting away the constness to later modify them is undefined behaviour  so you have to copy your const char  strings char by char into dynamically allocated char  strings in order to modify them   Example    include  lt iostream gt   void print char  ch    void print const char  ch        std  cout lt  lt ch     int main         print  Hello        return 0

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