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.token.entity { cursor: help }
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.language-json .token.property { color: rgba(24, 54, 145, 1) }
.language-markup .token.tag .token.punctuation { color: rgba(51, 51, 51, 1) }
code.language-css, .language-css .token.function { color: rgba(0, 134, 179, 1) }
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code.language-yaml { color: rgba(24, 54, 145, 1) }
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.language-markdown .token.url { color: rgba(121, 93, 163, 1) }
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.language-makefile .token.variable { color: rgba(24, 54, 145, 1) }
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.language-bash .token.keyword { color: rgba(0, 134, 179, 1) }
pre[data-line] { position: relative; padding: 1em 0 1em 3em }
pre[data-line] .line-highlight-wrapper { position: absolute; top: 0; left: 0; background-color: rgba(0, 0, 0, 0); display: block; width: 100% }
pre[data-line] .line-highlight { position: absolute; left: 0; right: 0; margin-top: 1em; background: linear-gradient(90deg, rgba(153, 122, 102, 0.1) 70%, rgba(153, 122, 102, 0)); pointer-events: none; line-height: inherit; white-space: pre }
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html body>:first-child { margin-top: 0 }
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html body h2 { font-size: 1.75em; font-weight: 400; padding-bottom: 0.3em }
html body h3 { font-size: 1.5em; font-weight: 500 }
html body h4 { font-size: 1.25em; font-weight: 600 }
html body h5 { font-size: 1.1em; font-weight: 600 }
html body h6 { font-size: 1em; font-weight: 600 }
html body h1, html body h2, html body h3, html body h4, html body h5 { font-weight: 600 }
html body h5 { font-size: 1em }
html body h6 { color: rgba(92, 92, 92, 1) }
html body strong { color: rgba(0, 0, 0, 1) }
html body del { color: rgba(92, 92, 92, 1) }
html body a:not([href]) { color: inherit; text-decoration: none }
html body a { color: rgba(0, 136, 204, 1); text-decoration: none }
html body a:hover { color: rgba(0, 163, 245, 1); text-decoration: none }
html body img { max-width: 100% }
html body>p { margin-top: 0; margin-bottom: 16px; word-wrap: break-word }
html body>ul, html body>ol { margin-bottom: 16px }
html body ul, html body ol { padding-left: 2em }
html body ul.no-list, html body ol.no-list { padding: 0; list-style-type: none }
html body ul ul, html body ul ol, html body ol ol, html body ol ul { margin-top: 0; margin-bottom: 0 }
html body li { margin-bottom: 0 }
html body li.task-list-item { list-style: none }
html body li>p { margin-top: 0; margin-bottom: 0 }
html body .task-list-item-checkbox { margin: 0 0.2em 0.25em -1.8em; vertical-align: middle }
html body .task-list-item-checkbox:hover { cursor: pointer }
html body blockquote { margin: 16px 0; font-size: inherit; padding: 0 15px; color: rgba(92, 92, 92, 1); border-left: 4px solid rgba(214, 214, 214, 1) }
html body blockquote>:first-child { margin-top: 0 }
html body blockquote>:last-child { margin-bottom: 0 }
html body hr { height: 4px; margin: 32px 0; background-color: rgba(214, 214, 214, 1); border: 0 none }
html body table { margin: 10px 0 15px; border-collapse: collapse; border-spacing: 0; display: block; width: 100%; overflow: auto; word-break: keep-all }
html body table th { font-weight: bold; color: rgba(0, 0, 0, 1) }
html body table td, html body table th { border: 1px solid rgba(214, 214, 214, 1); padding: 6px 13px }
html body dl { padding: 0 }
html body dl dt { padding: 0; margin-top: 16px; font-size: 1em; font-style: italic; font-weight: bold }
html body dl dd { padding: 0 16px; margin-bottom: 16px }
html body code { font-family: Menlo, Monaco, Consolas, "Courier New", monospace; font-size: 0.85em !important; color: rgba(0, 0, 0, 1); background-color: rgba(240, 240, 240, 1); border-radius: 3px; padding: 0.2em 0 }
html body code::before, html body code::after { letter-spacing: -0.2em; content: " " }
html body pre>code { padding: 0; margin: 0; font-size: 0.85em !important; word-break: normal; white-space: pre; background: rgba(0, 0, 0, 0); border: 0 }
html body .highlight { margin-bottom: 16px }
html body .highlight pre, html body pre { padding: 1em; overflow: auto; font-size: 0.85em !important; line-height: 1.45; border: rgba(214, 214, 214, 1); border-radius: 3px }
html body .highlight pre { margin-bottom: 0; word-break: normal }
html body pre code, html body pre tt { display: inline; max-width: initial; padding: 0; margin: 0; overflow: initial; line-height: inherit; word-wrap: normal; background-color: rgba(0, 0, 0, 0); border: 0 }
html body pre code:before, html body pre tt:before, html body pre code:after, html body pre tt:after { content: normal }
html body p, html body blockquote, html body ul, html body ol, html body dl, html body pre { margin-top: 0; margin-bottom: 16px }
html body kbd { color: rgba(0, 0, 0, 1); border-top: 1px solid rgba(214, 214, 214, 1); border-right: 1px solid rgba(214, 214, 214, 1); border-bottom: 2px solid rgba(199, 199, 199, 1); border-left: 1px solid rgba(214, 214, 214, 1); padding: 2px 4px; background-color: rgba(240, 240, 240, 1); border-radius: 3px }
@media print { html body { background-color: rgba(255, 255, 255, 1) } html body h1, html body h2, html body h3, html body h4, html body h5, html body h6 { color: rgba(0, 0, 0, 1); page-break-after: avoid } html body blockquote { color: rgba(92, 92, 92, 1) } html body pre { page-break-inside: avoid } html body table { display: table } html body img { display: block; max-width: 100%; max-height: 100% } html body pre, html body code { word-wrap: break-word; white-space: pre } }
.markdown-preview { width: 100%; height: 100%; box-sizing: border-box }
.markdown-preview .pagebreak, .markdown-preview .newpage { page-break-before: always }
.markdown-preview pre.line-numbers { position: relative; padding-left: 3.8em; counter-reset: linenumber 0 }
.markdown-preview pre.line-numbers>code { position: relative }
.markdown-preview pre.line-numbers .line-numbers-rows { position: absolute; pointer-events: none; top: 1em; font-size: 100%; left: 0; width: 3em; letter-spacing: -1px; border-right: 1px solid rgba(153, 153, 153, 1); -webkit-user-select: none; -moz-user-select: none; -ms-user-select: none; user-select: none }
.markdown-preview pre.line-numbers .line-numbers-rows>span { pointer-events: none; display: block; counter-increment: linenumber 1 }
.markdown-preview pre.line-numbers .line-numbers-rows>span:before { content: counter(linenumber); color: rgba(153, 153, 153, 1); display: block; padding-right: 0.8em; text-align: right }
.markdown-preview .mathjax-exps .MathJax_Display { text-align: center !important }
.markdown-preview:not([for="preview"]) .code-chunk .btn-group { display: none }
.markdown-preview:not([for="preview"]) .code-chunk .status { display: none }
.markdown-preview:not([for="preview"]) .code-chunk .output-div { margin-bottom: 16px }
{ width: 8px }
{ border-radius: 10px; background-color: rgba(0, 0, 0, 0) }
{ border-radius: 5px; background-color: rgba(150, 150, 150, 0.66); border: 4px solid rgba(150, 150, 150, 0.66); background-clip: content-box }
html body[for="html-export"]:not([data-presentation-mode]) { position: relative; width: 100%; height: 100%; top: 0; left: 0; margin: 0; padding: 0; overflow: auto }
html body[for="html-export"]:not([data-presentation-mode]) .markdown-preview { position: relative; top: 0 }
@media screen and (min-width: 914px) { html body[for="html-export"]:not([data-presentation-mode]) .markdown-preview { padding: 2em calc(50% - 457px + 2em) } }
@media screen and (max-width: 914px) { html body[for="html-export"]:not([data-presentation-mode]) .markdown-preview { padding: 2em } }
@media screen and (max-width: 450px) { html body[for="html-export"]:not([data-presentation-mode]) .markdown-preview { font-size: 14px !important; padding: 1em } }
@media print { html body[for="html-export"]:not([data-presentation-mode]) #sidebar-toc-btn { display: none } }
html body[for="html-export"]:not([data-presentation-mode]) #sidebar-toc-btn { position: fixed; bottom: 8px; left: 8px; font-size: 28px; cursor: pointer; color: inherit; z-index: 99; width: 32px; text-align: center; opacity: 0.4 }
html body[for="html-export"]:not([data-presentation-mode])[html-show-sidebar-toc] #sidebar-toc-btn { opacity: 1 }
html body[for="html-export"]:not([data-presentation-mode])[html-show-sidebar-toc] .md-sidebar-toc { position: fixed; top: 0; left: 0; width: 300px; height: 100%; padding: 32px 0 48px; font-size: 14px; box-shadow: 0 0 4px rgba(150, 150, 150, 0.33); box-sizing: border-box; overflow: auto; background-color: inherit }
{ width: 8px }
{ border-radius: 10px; background-color: rgba(0, 0, 0, 0) }
{ border-radius: 5px; background-color: rgba(150, 150, 150, 0.66); border: 4px solid rgba(150, 150, 150, 0.66); background-clip: content-box }
html body[for="html-export"]:not([data-presentation-mode])[html-show-sidebar-toc] .md-sidebar-toc a { text-decoration: none }
html body[for="html-export"]:not([data-presentation-mode])[html-show-sidebar-toc] .md-sidebar-toc ul { padding: 0 1.6em; margin-top: 0.8em }
html body[for="html-export"]:not([data-presentation-mode])[html-show-sidebar-toc] .md-sidebar-toc li { margin-bottom: 0.8em }
html body[for="html-export"]:not([data-presentation-mode])[html-show-sidebar-toc] .md-sidebar-toc ul { list-style-type: none }
html body[for="html-export"]:not([data-presentation-mode])[html-show-sidebar-toc] .markdown-preview { left: 300px; width: calc(100% - 300px); padding: 2em calc(50% - 457px - 150px); margin: 0; box-sizing: border-box }
@media screen and (max-width: 1274px) { html body[for="html-export"]:not([data-presentation-mode])[html-show-sidebar-toc] .markdown-preview { padding: 2em } }
@media screen and (max-width: 450px) { html body[for="html-export"]:not([data-presentation-mode])[html-show-sidebar-toc] .markdown-preview { width: 100% } }
html body[for="html-export"]:not([data-presentation-mode]):not([html-show-sidebar-toc]) .markdown-preview { left: 50%; transform: translateX(-50%) }
html body[for="html-export"]:not([data-presentation-mode]):not([html-show-sidebar-toc]) .md-sidebar-toc { display: none }

定义

  • 函数覆盖

    (1) 作用域不同

    (2) 有virtual关键字

    (3) 参数列表/返回值/调用约定必须相同
  • 函数隐藏

    (1) 作用域不同

    (2) 函数名相同

    (3) 参数列表/返回值/调用约定不考虑
  • 函数重载

    (1) 作用域相同

    (2) 函数名相同

    (3) 参数列表不同,返回值/调用约定不考

练习

class Base
{
public:
virtual void Handle1(float x)
{
cout << "Base::Handle1(float) " << x << endl;
}
void Handle2(float x)
{
cout << "Base::Handle2(float) " << x << endl;
}
void Handle3(float x)
{
cout << "Base::Handle3(float) " << x << endl;
}
}; class Derived : public Base
{
public:
virtual void Handle1(float x)
{
cout << "Derived::Handle1(float) " << x << endl;
}
void Handle2(int x)
{
cout << "Derived::Handle2(int) " << x << endl;
}
void Handle3(float x)
{
cout << "Derived::Handle3(float) " << x << endl;
}
void Handle3(double x)
{
cout << "Derived::Handle3(double) " << x << endl;
}
};

观察以上类声明及实现,试预测以下main中的执行结果,注意两点:

  1. 调用的方法是哪个?
  2. 调用造成的原因,是重载、覆盖、隐藏中的哪一种?
 void main(void)
{
Derived DervObj;
Base *pBase = &DervObj;
Derived *pDerv = &DervObj; pBase->Handle1(3.14f);
/******************************************
预测:
输出Derived::Handle1(float)3.14
是间接调用,覆盖
运行结果:Derived::Handle1(float)3.14
******************************************/ pDerv->Handle1(3.14f);
cout << endl;
/******************************************
预测:
输出Derived::Handle1(float)3.14
是间接调用,隐藏
运行结果:Derived::Handle1(float)3.14
******************************************/ pBase->Handle2(3.14f);
/*****************************************
预测:
输出Base::Handle2(float)3.14
是直接调用,隐藏
运行结果:Base::Handle2(float)3.14
*****************************************/ pDerv->Handle2(3.14f);
/****************************************
预测:
输出Derived::Handle2(int)3
是直接调用,隐藏
运行结果:Derived::Handle2(int)3
*****************************************/
cout << endl; pBase->Handle3(3.14f);
/****************************************
预测:
输出Base::Handle3(float)3.14
直接调用,隐藏
结果:Base::Handle3(float) 3.14
}
****************************************/ pDerv->Handle3(3.14f);
/***************************************
预测:输出Derived::Handle3(float)3.14
直接调用,隐藏
结果:Derived::Handle3(float) 3.14
}
***************************************/ pDerv->Handle3(3.14);
/**************************************
预测:输出Derived::Handle3(double)3.14
直接调用,隐藏
结果:Derived::Handle3(double) 3.14
**************************************/
cout << endl; pDerv->Handle3(3);
/****************************************
Handle3没有对应的整数形参,只有float和double
3既可以转换为float,又可以转换为double,所以编译时报错。
/****************************************/
system("pause");
}

总结

当覆盖,隐藏,重载同时存在时,如何确定调用了某个类的某个函数?

a)查看调用该函数的数据类型,并找到该类型的作用域(函数隐藏)

b)在该作用域中找到同名函数,满足参数列表相同(可以做适当的类型转换),在从这些同名函数中选出最佳的,

如果有多个则产生二义性(函数重载)

c)查看选出的最佳匹配函数是否是虚函数,如果是虚函数并且调用该虚函数的数据类型为指针或引用,

那么就是间接调用,否则就是直接调用(函数覆盖)

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