I tried to compile following program with gcc.
0 #include <stdio.h>
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 < 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开发者_开发百科 explain why the problem happens? Thanks!
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.
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.
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.
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