C++编译时多态是如何实现的呢？（名字粉碎机制）

一.在C++中我们可能会使用到很多同名但是底层时如何识的呢？

在linux环境下，我们可以查看汇编代码，这个是我们的源代码。

#include 
int  swap1(int a,int  b){
    int temp = a;
    a = b;
    b = temp;
    return 0;
}
double  swap1(double a,double  b){
    double temp = a;
    a = b;
    b = temp;
    return 2.0;
}
int main(){
    swap1(1,2);
    swap1(1.0,2.0);
    return 0;
}

我们可以看到有两个同名不同参的函数，然后我们将此文件进行编译。我们来看一下汇编代码。

	.file	"test.cpp"
	.text
	.local	_ZStL8__ioinit
	.comm	_ZStL8__ioinit,1,1
	.globl	_Z5swap1ii
	.type	_Z5swap1ii, @function
_Z5swap1ii:
.LFB1731:
	.cfi_startproc
	endbr64
	pushq	%rbp
	.cfi_def_cfa_offset 16
	.cfi_offset 6, -16
	movq	%rsp, %rbp
	.cfi_def_cfa_register 6
	movl	%edi, -20(%rbp)
	movl	%esi, -24(%rbp)
	movl	-20(%rbp), %eax
	movl	%eax, -4(%rbp)
	movl	-24(%rbp), %eax
	movl	%eax, -20(%rbp)
	movl	-4(%rbp), %eax
	movl	%eax, -24(%rbp)
	movl	$0, %eax
	popq	%rbp
	.cfi_def_cfa 7, 8
	ret
	.cfi_endproc
.LFE1731:
	.size	_Z5swap1ii, .-_Z5swap1ii
	.globl	_Z5swap1dd
	.type	_Z5swap1dd, @function
_Z5swap1dd:
.LFB1732:
	.cfi_startproc
	endbr64
	pushq	%rbp
	.cfi_def_cfa_offset 16
	.cfi_offset 6, -16
	movq	%rsp, %rbp
	.cfi_def_cfa_register 6
	movsd	%xmm0, -24(%rbp)
	movsd	%xmm1, -32(%rbp)
	movsd	-24(%rbp), %xmm0
	movsd	%xmm0, -8(%rbp)
	movsd	-32(%rbp), %xmm0
	movsd	%xmm0, -24(%rbp)
	movsd	-8(%rbp), %xmm0
	movsd	%xmm0, -32(%rbp)
	movsd	.LC0(%rip), %xmm0
	movq	%xmm0, %rax
	movq	%rax, %xmm0
	popq	%rbp
	.cfi_def_cfa 7, 8
	ret
	.cfi_endproc
.LFE1732:
	.size	_Z5swap1dd, .-_Z5swap1dd
	.globl	main
	.type	main, @function
main:
.LFB1733:
	.cfi_startproc
	endbr64
	pushq	%rbp
	.cfi_def_cfa_offset 16
	.cfi_offset 6, -16
	movq	%rsp, %rbp
	.cfi_def_cfa_register 6
	movl	$2, %esi
	movl	$1, %edi
	call	_Z5swap1ii
	movsd	.LC0(%rip), %xmm0
	movq	.LC1(%rip), %rax
	movapd	%xmm0, %xmm1
	movq	%rax, %xmm0
	call	_Z5swap1dd
	movl	$0, %eax
	popq	%rbp
	.cfi_def_cfa 7, 8
	ret
	.cfi_endproc
.LFE1733:
	.size	main, .-main
	.type	_Z41__static_initialization_and_destruction_0ii, @function
_Z41__static_initialization_and_destruction_0ii:
.LFB2228:
	.cfi_startproc
	endbr64
	pushq	%rbp
	.cfi_def_cfa_offset 16
	.cfi_offset 6, -16
	movq	%rsp, %rbp
	.cfi_def_cfa_register 6
	subq	$16, %rsp
	movl	%edi, -4(%rbp)
	movl	%esi, -8(%rbp)
	cmpl	$1, -4(%rbp)
	jne	.L9
	cmpl	$65535, -8(%rbp)
	jne	.L9
	leaq	_ZStL8__ioinit(%rip), %rax
	movq	%rax, %rdi
	call	_ZNSt8ios_base4InitC1Ev@PLT
	leaq	__dso_handle(%rip), %rax
	movq	%rax, %rdx
	leaq	_ZStL8__ioinit(%rip), %rax
	movq	%rax, %rsi
	movq	_ZNSt8ios_base4InitD1Ev@GOTPCREL(%rip), %rax
	movq	%rax, %rdi
	call	__cxa_atexit@PLT
.L9:
	nop
	leave
	.cfi_def_cfa 7, 8
	ret
	.cfi_endproc
.LFE2228:
	.size	_Z41__static_initialization_and_destruction_0ii, .-_Z41__static_initialization_and_destruction_0ii
	.type	_GLOBAL__sub_I__Z5swap1ii, @function
_GLOBAL__sub_I__Z5swap1ii:
.LFB2229:
	.cfi_startproc
	endbr64
	pushq	%rbp
	.cfi_def_cfa_offset 16
	.cfi_offset 6, -16
	movq	%rsp, %rbp
	.cfi_def_cfa_register 6
	movl	$65535, %esi
	movl	$1, %edi
	call	_Z41__static_initialization_and_destruction_0ii
	popq	%rbp
	.cfi_def_cfa 7, 8
	ret
	.cfi_endproc
.LFE2229:
	.size	_GLOBAL__sub_I__Z5swap1ii, .-_GLOBAL__sub_I__Z5swap1ii
	.section	.init_array,"aw"
	.align 8
	.quad	_GLOBAL__sub_I__Z5swap1ii
	.section	.rodata
	.align 8
.LC0:
	.long	0
	.long	1073741824
	.align 8
.LC1:
	.long	0
	.long	1072693248
	.hidden	__dso_handle
	.ident	"GCC: (Ubuntu 11.3.0-1ubuntu1~22.04) 11.3.0"
	.section	.note.GNU-stack,"",@progbits
	.section	.note.gnu.property,"a"
	.align 8
	.long	1f - 0f
	.long	4f - 1f
	.long	5
0:
	.string	"GNU"
1:
	.align 8
	.long	0xc0000002
	.long	3f - 2f
2:
	.long	0x3
3:
	.align 8
4:

我们可以从中看到两个相似的东西

        _Z5swap1dd:

        _Z5swap1ii:

        这个就是我们的两个函数，5就是说函数名时五个字符（博主没学过汇编，_Z可能时返回值，swap1是我们的函数名，dd和ii分别时我们形参的类型，大家自己去试试其他的）