Ternary operator usage error, "ERROR:void value not ignored as it ought to be"

Question

(choice=='Y'||choice=='y')?((printf("\n...The program is now resetting...\n")&&(main()))):((printf("\n\tThank you for trying out the BPCC App.\n"))&&(exit(0)));

如果我删除 exit(0) 整个程序运行正常，但我需要包括 exit(0)。

你能帮帮我吗？

Answer 1

来自 C11 标准，第 6.5.13 章，逻辑与 [&&] 运算符

Each of the operands shall have scalar type.

和来自exit()的man page

void exit(int status);

现在，void 不是有效值（或标量类型）。所以，你不能写

...:((printf("\n\tThank you for trying out the BPCC App.\n"))&&(exit(0)));
                                                               |--------|
                                        The return value of `exit()` is used
                                            as one of the operands of `&&` here

因此出现错误。您不能使用 exit() 的 return 值 来编写逻辑（基本上有什么意义？）。你必须想出一些替代方案。（就像调用 exit() 作为下一条指令或类似指令）。正如 @BLUEPIXY 先生在中提到的，一种可能的方法是使用 comma 运算符 [,]，如下所示

.... (printf("\n\tThank you for trying out the BPCC App.\n")) , (exit(0))

也就是说，这种方法（递归调用 main()）不是一个好的做法。

Answer 2

试试这个

(printf("message") && (exit(0),1))

或

(printf("message") , exit(0))

Answer 3

函数exit声明如下

_Noreturn void exit(int status);

所以你不能在这样的表达式中使用它

(printf("\n\tThank you for trying out the BPCC App.\n"))&&(exit(0))

您可以使用逗号运算符代替运算符 &&。

因此三元运算符可以如下所示

( choice == 'Y' || choice == 'y' ) 
   ? ( printf( "\n...The program is now resetting...\n" ) , ( void )main() )
   : ( printf( "\n\tThank you for trying out the BPCC App.\n" ), exit( 0 ) );

或以下方式

( choice == 'Y' || choice == 'y' ) 
   ? ( printf( "\n...The program is now resetting...\n" ) , exit( main() ) )
   : ( printf( "\n\tThank you for trying out the BPCC App.\n" ), exit( 0 ) );

Ternary operator usage error, "ERROR:void value not ignored as it ought to be"

Ternary operator usage error, "ERROR:void value not ignored as it ought to be"

c

logical-and