[请教]关于gcc和cc编译工具编译的不同结果

nashi2000

代码例子:
#include<stdio.h>
//void my_print(char *string);
//void my_print2(char *string);
main()
{
    char my_string[]="hello there";
    my_print( my_string );
    my_print2( my_string );
}
void my_print(char *string)
{
    printf("The string is %s\n",string);
}
void my_print2(char *string)
{
    char *string2;
    int size,i;
    size=strlen(string);
    string2=(char*)malloc(size+1);
    for(i=0;i<size;i++)
        string2[size-1-i]=string[i];
    string2[size]='\0';
    printf("The string printed backward is %s\n", string2);
}

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用cc编译c代码时,如果调用了没有事先声明的函数,会报告错误:
$ cc greet.c
"greet.c", line 9: identifier redeclared: my_print
        current : function(pointer to char) returning void
        previous: function() returning int : "greet.c", line 5
"greet.c", line 13: identifier redeclared: my_print2
        current : function(pointer to char) returning void
        previous: function() returning int : "greet.c", line 6
cc: acomp failed for greet.c
----------------------------------------------------------------------
但是用gcc编译,只是会产生warning:
$ gcc greet.c
greet.c:9: warning: type mismatch with previous implicit declaration
greet.c:5: warning: previous implicit declaration of `my_print'
greet.c:9: warning: `my_print' was previously implicitly declared to return `int'
greet.c:13: warning: type mismatch with previous implicit declaration
greet.c:6: warning: previous implicit declaration of `my_print2'
greet.c:13: warning: `my_print2' was previously implicitly declared to return `int'
===========================================================
请问一下,这是什么原因。这种情况是不是cc可以通过增加什么选项,来完成类似代码的编译。