C++学习笔记之 初识与概述

概述

C++ = C + 面向对象编程 + 泛型编程

C语言是面向过程的，C++是面向对象的

初识

Hello world

#include <iostream> // 导入库，不需要.h后缀
// iostream 即标准输入输出流

int main()
{
    std::cout << "Hello world
"; // 这里留到后面讲

    return 0;
}

Hello world

对比

C语言Hello world

#include <stdio.h>

int main()
{
    printf("Hello world
");

    return 0;
}

汇编代码：

	.file	"test.c"
	.text
	.def	___main;	.scl	2;	.type	32;	.endef
	.section .rdata,"dr"
LC0:
	.ascii "Hello world"
	.text
	.globl	_main
	.def	_main;	.scl	2;	.type	32;	.endef
_main:
LFB13:
	.cfi_startproc
	pushl	%ebp
	.cfi_def_cfa_offset 8
	.cfi_offset 5, -8
	movl	%esp, %ebp
	.cfi_def_cfa_register 5
	andl	$-16, %esp
	subl	$16, %esp
	call	___main
	movl	$LC0, (%esp)
	call	_puts
	movl	$0, %eax
	leave
	.cfi_restore 5
	.cfi_def_cfa 4, 4
	ret
	.cfi_endproc
LFE13:
	.ident	"GCC: (MinGW.org GCC Build-2) 9.2.0"
	.def	_puts;	.scl	2;	.type	32;	.endef

共计31行

C++

	.file	"main.cpp"
	.text
	.section .rdata,"dr"
__ZStL19piecewise_construct:
	.space 1
.lcomm __ZStL8__ioinit,1,1
	.def	___main;	.scl	2;	.type	32;	.endef
LC0:
	.ascii "Hello world12"
	.text
	.globl	_main
	.def	_main;	.scl	2;	.type	32;	.endef
_main:
LFB1511:
	.cfi_startproc
	pushl	%ebp
	.cfi_def_cfa_offset 8
	.cfi_offset 5, -8
	movl	%esp, %ebp
	.cfi_def_cfa_register 5
	andl	$-16, %esp
	subl	$16, %esp
	call	___main
	movl	$LC0, 4(%esp)
	movl	$__ZSt4cout, (%esp)
	call	__ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc
	movl	$0, %eax
	leave
	.cfi_restore 5
	.cfi_def_cfa 4, 4
	ret
	.cfi_endproc
LFE1511:
	.def	___tcf_0;	.scl	3;	.type	32;	.endef
___tcf_0:
LFB1984:
	.cfi_startproc
	pushl	%ebp
	.cfi_def_cfa_offset 8
	.cfi_offset 5, -8
	movl	%esp, %ebp
	.cfi_def_cfa_register 5
	subl	$8, %esp
	movl	$__ZStL8__ioinit, %ecx
	call	__ZNSt8ios_base4InitD1Ev
	leave
	.cfi_restore 5
	.cfi_def_cfa 4, 4
	ret
	.cfi_endproc
LFE1984:
	.def	__Z41__static_initialization_and_destruction_0ii;	.scl	3;	.type	32;	.endef
__Z41__static_initialization_and_destruction_0ii:
LFB1983:
	.cfi_startproc
	pushl	%ebp
	.cfi_def_cfa_offset 8
	.cfi_offset 5, -8
	movl	%esp, %ebp
	.cfi_def_cfa_register 5
	subl	$24, %esp
	cmpl	$1, 8(%ebp)
	jne	L6
	cmpl	$65535, 12(%ebp)
	jne	L6
	movl	$__ZStL8__ioinit, %ecx
	call	__ZNSt8ios_base4InitC1Ev
	movl	$___tcf_0, (%esp)
	call	_atexit
L6:
	nop
	leave
	.cfi_restore 5
	.cfi_def_cfa 4, 4
	ret
	.cfi_endproc
LFE1983:
	.def	__GLOBAL__sub_I_main;	.scl	3;	.type	32;	.endef
__GLOBAL__sub_I_main:
LFB1985:
	.cfi_startproc
	pushl	%ebp
	.cfi_def_cfa_offset 8
	.cfi_offset 5, -8
	movl	%esp, %ebp
	.cfi_def_cfa_register 5
	subl	$24, %esp
	movl	$65535, 4(%esp)
	movl	$1, (%esp)
	call	__Z41__static_initialization_and_destruction_0ii
	leave
	.cfi_restore 5
	.cfi_def_cfa 4, 4
	ret
	.cfi_endproc
LFE1985:
	.section	.ctors,"w"
	.align 4
	.long	__GLOBAL__sub_I_main
	.ident	"GCC: (MinGW.org GCC Build-2) 9.2.0"
	.def	__ZStlsISt11char_traitsIcEERSt13basic_ostreamIcT_ES5_PKc;	.scl	2;	.type	32;	.endef
	.def	__ZNSt8ios_base4InitD1Ev;	.scl	2;	.type	32;	.endef
	.def	__ZNSt8ios_base4InitC1Ev;	.scl	2;	.type	32;	.endef
	.def	_atexit;	.scl	2;	.type	32;	.endef

共计104行

结论：C++在编译速度和运行速度上都会相对的慢于C语言