(1){}与(1)是否相同;

I just want to be sure that this C code:

我只是想确定这个C代码:

while(flag==true)
{
} 
foo();

does the same as this:

做同样的事情:

while(flag==true);

foo();

6 个解决方案

#1

; alone is a null statement in C.

;单独是C中的空语句。

In your case, {} or ; are syntactically needed, but they do the same: nothing

在你的情况下，{};在句法上是需要的，但它们做的是一样的:什么都不做

Related: Use of null statement in C

#2

In addition to the other answers: It's the same thing.

除了其他答案:这是一样的。

But I prefer this:

但我更喜欢这个:

while (condition)
{
} 
foo();

over this:

在这:

while (condition);
foo();

because if you forget the semicolon after the while, your code will compile fine but it won't do what you expect:

因为如果您在之后忘记了分号，那么您的代码可以很好地编译，但是它不会做您期望的事情:

while(condition)  // ; forgotten here
foo();

will actually be equivalent of:

实际上等于:

while(condition)
{
  foo();
}

#3

Yes, having an empty body of the loop is equivaled to just while(<some condition>);

是的，循环的空体等于just while( <某个条件> );

#4

Yes. A ; following a control structure (e.g., while, for, etc.) that can be followed with a block is treated as if it was followed by an empty block.

是的。一个;可以使用块跟随的控制结构(例如while、for等)被视为后面跟着一个空块。

#5

Yes, because when put semicolon after while loop statement that indicate empty body and when the condition becomes false then it goes to the immediate next statement after that loop.

是的，因为当在while循环语句后面加上分号表示空体时，当条件变为false时，它就会转到循环之后的下一个语句。

#6

Yes, they are same.

是的,它们是一样的。

You Can Generate The assembly of the code and see for yourself that they produce the same assembly. (Using gcc filename.c -S -masm=intel -o ouputfilename)

您可以生成代码的程序集，并亲自查看它们是否生成相同的程序集。(使用gcc文件名。c -S -masm=intel -o ouputfilename)

#include<stdio.h>

int foo(void);
int main(){

  int flag;
  scanf("%d" , &flag);
  while(flag==1);
  foo(); 
}


int foo(void){
  int x = 2;
  return x*x;
}

.LC0:
    .ascii "%d\0"
    .text
    .globl  main
    .def    main;   .scl    2;  .type   32; .endef
    .seh_proc   main
main:
    push    rbp
    .seh_pushreg    rbp
    mov rbp, rsp
    .seh_setframe   rbp, 0
    sub rsp, 48
    .seh_stackalloc 48
    .seh_endprologue
    call    __main
    lea rax, -4[rbp]
    mov rdx, rax
    lea rcx, .LC0[rip]
    call    scanf
    nop
.L2:
    mov eax, DWORD PTR -4[rbp]
    cmp eax, 1
    je  .L2
    call    foo
    mov eax, 0
    add rsp, 48
    pop rbp
    ret
    .seh_endproc
    .globl  foo
    .def    foo;    .scl    2;  .type   32; .endef
    .seh_proc   foo
foo:
    push    rbp
    .seh_pushreg    rbp
    mov rbp, rsp
    .seh_setframe   rbp, 0
    sub rsp, 16
    .seh_stackalloc 16
    .seh_endprologue
    mov DWORD PTR -4[rbp], 2
    mov eax, DWORD PTR -4[rbp]
    imul    eax, DWORD PTR -4[rbp]
    add rsp, 16
    pop rbp
    ret
    .seh_endproc
    .ident  "GCC: (x86_64-posix-seh-rev1, Built by MinGW-W64 project) 6.3.0"
    .def    scanf;  .scl    2;  .type   32; .endef

And When I Changed while(flag == 1); to while(flag==1){} Assembly Code Generated is :

当我改变时(flag = 1)到while(flag==1){}汇编代码生成:

.LC0:
    .ascii "%d\0"
    .text
    .globl  main
    .def    main;   .scl    2;  .type   32; .endef
    .seh_proc   main
main:
    push    rbp
    .seh_pushreg    rbp
    mov rbp, rsp
    .seh_setframe   rbp, 0
    sub rsp, 48
    .seh_stackalloc 48
    .seh_endprologue
    call    __main
    lea rax, -4[rbp]
    mov rdx, rax
    lea rcx, .LC0[rip]
    call    scanf
    nop
.L2:
    mov eax, DWORD PTR -4[rbp]
    cmp eax, 1
    je  .L2
    call    foo
    mov eax, 0
    add rsp, 48
    pop rbp
    ret
    .seh_endproc
    .globl  foo
    .def    foo;    .scl    2;  .type   32; .endef
    .seh_proc   foo
foo:
    push    rbp
    .seh_pushreg    rbp
    mov rbp, rsp
    .seh_setframe   rbp, 0
    sub rsp, 16
    .seh_stackalloc 16
    .seh_endprologue
    mov DWORD PTR -4[rbp], 2
    mov eax, DWORD PTR -4[rbp]
    imul    eax, DWORD PTR -4[rbp]
    add rsp, 16
    pop rbp
    ret
    .seh_endproc
    .ident  "GCC: (x86_64-posix-seh-rev1, Built by MinGW-W64 project) 6.3.0"
    .def    scanf;  .scl    2;  .type   32; .endef

You can see that the relevant portion is same in both cases.

您可以看到，在这两种情况下，相关的部分是相同的。

 //Below Portion is same in both cases. 
.L2:        
    mov eax, DWORD PTR -4[rbp]
    cmp eax, 1
    je  .L2
    call    foo
    mov eax, 0
    add rsp, 48
    pop rbp
    ret
    .seh_endproc
    .globl  foo
    .def    foo;    .scl    2;  .type   32; .endef
    .seh_proc   foo

#1