GCC 会编译，但 clang 不会

Question

So in my finals there was an exercise asking what will the program print.

This is the code:

#include <stdio.h>

int main (){
    int x=5, y=4;

    if (x>y);
      printf("A");

    if(x=4)
      printf("%d",x+y);

     return 0;
}

When I try to compile it using gcc -ansi -pedantic -Werror on a Debian machine, it compiles just fine and outputs "A8".

However, when I try to compile it using clang -ansi -pedantic -Werror , I receive errors regarding the if (x=4) expression missing = and missing statement on if(x>y); .

Why does that happen, and which answer could be marked as correct?

Answer 1

compilers may emit different warnings. For example clang warns about empty statement and gcc does not.

So if you set -Werror it will compile using gcc but will not compile using the clang.

BTW what is stopping you from reading the compiler messages. They are self-explanatory. It even shows how to correct it.

#1 with x86-64 clang 9.0.0

<source>:6:9: error: if statement has empty body [-Werror,-Wempty-body]

if (x>y);

        ^

<source>:6:9: note: put the semicolon on a separate line to silence this warning

<source>:8:5: error: using the result of an assignment as a condition without parentheses [-Werror,-Wparentheses]

if(x=4)

   ~^~

<source>:8:5: note: place parentheses around the assignment to silence this warning

if(x=4)

    ^

   (  )

<source>:8:5: note: use '==' to turn this assignment into an equality comparison

if(x=4)

    ^

    ==

<source>:12:2: error: no newline at end of file [-Werror,-Wnewline-eof]

}

 ^

3 errors generated.

Compiler returned: 1