conflicting types error when compiling c program using gcc

Question

I tried to compile following program with gcc    0  include   lt stdio h gt  1  2 main    3 4       5  char my string      hello there         6 7  my print  my string       8  my print2  my string       9  10    11 void my print  char  string  12       13  printf   The string is  s n   string       14   15         16 void my print2  char  string  17   18  char  string2      19  int size  i     20 21  size   strlen  string       22  string2    char    malloc  size   1   23 24  for  i   0  i  lt  size  i        25    string2 size - i    string i   26 27   string2 size 1      0       28   printf   The string printed backward is  s n   string2       29     However  it fails and the compiler produces following error log    greeting c  11  error conflicting types for  my print  greeting c  7  error  previous implicit declaration of  my print  was here greeting c  16  error conflicting types for  my print2  greeting c 8  erroro previous implicit declaration of  my print2  was there   And if I move the my print and my print2 functions before the main function  everything goes well  So can anyone explain why the problem happens  Thanks

User · Answer

You have to declare your functions before main      or declare the function prototypes before main     As it is  the compiler sees my print  my string   in main   as a function declaration   Move your functions above main   in the file  or put   void my print  char     void my print2  char       Above main   in the file

User · Answer

If you don t declare a function and it only appears after being called  it is automatically assumed to be int  so in your case  you didn t declare  void my print  char     void my print2  char       before you call it in main  so the compiler assume there are functions which their prototypes are int my print2  char     and int my print2  char     and you can t have two functions with the same prototype except of the return type  so you get the error of conflicting types   As Brian suggested  declare those two methods before main

User · Answer

To answer a more generic case  this error is noticed when you pick a function name which is already used in some built in library  For e g   select    A simple method to know about it is while compiling the file  the compiler will indicate the previous declaration

[c] conflicting types error when compiling c program using gcc

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