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为什么我时不时会看到「珍惜生命，远离 C++」？ 第1页

  1 

user avatar   wywzxxz 网友的相关建议: 
      

竟然没人举实例，我给一个吧……

       1.#include"stdio.h" 2.#include"sparsepp-master/sparsepp.h" 3.int main() 4.{ 5. spp::sparse_hash_map<std::pair<int,int>,int> mp;  6.mp.insert(std::make_pair(std::make_pair(1,1),1));  7.return 0; 8.}

这个程序时使用sparsepp库提供的hash版map来存数据的例子，但他有一个错误：库中并没有给出为std::pair<int,int>产生hash值的算法，因此该程序不能工作。

理想情况下我们想要编译器这么提示我们：“亲爱的程序员，您的程序这里有错，错误原因和解决方法我都给你标注好了，么么嗒~~~”

具体错误提示大概长这样：

       line 6:mp.insert(std::make_pair(std::make_pair(1,1),1));                                 ^^^^^^^^^^^^^^^^^^^ can't generate serialization

但实际上有点困难，一般编译器只会这么提示我们：“吔屎啦，这里这里这里这里这里这里我都看不懂，赶紧给老娘改！”

JAVA和javascript就喜欢这么干，错误提示大概长这样：

       In file sparsepp-master/sparsepp.h:1483:42: XXXXXX In file sparsepp-master/sparsepp.h:5069:77: XXXXXX In file main.cpp:6:25: type cast failed In file main.cpp:3:1: XXXXX


而混乱邪恶的C++是这样提示我们的：


       In file included from main.cpp:2:0: sparsepp-master/sparsepp.h: In instantiation of 'size_t spp::spp_hash<T>::op erator()(const T&) const [with T = std::pair<int, int>; size_t = long long u nsigned int]': sparsepp-master/sparsepp.h:1483:42:   required from 'size_t spp::sparsehash_ internal::sh_hashtable_settings<Key, HashFunc, SizeType, HT_MIN_BUCKETS>::ha sh(const key_type&) const [with Key = std::pair<int, int>; HashFunc = spp::s pp_hash<std::pair<int, int> >; SizeType = long long unsigned int; int HT_MIN _BUCKETS = 4; size_t = long long unsigned int; spp::sparsehash_internal::sh_ hashtable_settings<Key, HashFunc, SizeType, HT_MIN_BUCKETS>::key_type = std: :pair<int, int>]' sparsepp-master/sparsepp.h:4729:31:   required from 'size_t spp::sparse_hash table<Value, Key, HashFcn, ExtractKey, SetKey, EqualKey, Alloc>::hash(const  key_type&) const [with Value = std::pair<std::pair<int, int>, int>; Key = st d::pair<int, int>; HashFcn = spp::spp_hash<std::pair<int, int> >; ExtractKey  = spp::sparse_hash_map<std::pair<int, int>, int>::SelectKey; SetKey = spp:: sparse_hash_map<std::pair<int, int>, int>::SetKey; EqualKey = std::equal_to< std::pair<int, int> >; Alloc = spp::libc_allocator_with_realloc<std::pair<co nst std::pair<int, int>, int> >; size_t = long long unsigned int; spp::spars e_hashtable<Value, Key, HashFcn, ExtractKey, SetKey, EqualKey, Alloc>::key_t ype = std::pair<int, int>]' sparsepp-master/sparsepp.h:4242:33:   required from 'spp::sparse_hashtable<V alue, Key, HashFcn, ExtractKey, SetKey, EqualKey, Alloc>::Position spp::spar se_hashtable<Value, Key, HashFcn, ExtractKey, SetKey, EqualKey, Alloc>::_fin d_position(const key_type&) const [with Value = std::pair<std::pair<int, int >, int>; Key = std::pair<int, int>; HashFcn = spp::spp_hash<std::pair<int, i nt> >; ExtractKey = spp::sparse_hash_map<std::pair<int, int>, int>::SelectKe y; SetKey = spp::sparse_hash_map<std::pair<int, int>, int>::SetKey; EqualKey  = std::equal_to<std::pair<int, int> >; Alloc = spp::libc_allocator_with_rea lloc<std::pair<const std::pair<int, int>, int> >; spp::sparse_hashtable<Valu e, Key, HashFcn, ExtractKey, SetKey, EqualKey, Alloc>::key_type = std::pair< int, int>]' sparsepp-master/sparsepp.h:4401:38:   required from 'std::pair<typename spp: :sparsetable<Value, typename Alloc::rebind<Value>::other>::ne_iterator, bool > spp::sparse_hashtable<Value, Key, HashFcn, ExtractKey, SetKey, EqualKey, A lloc>::_insert_noresize(T&) [with T = const std::pair<const std::pair<int, i nt>, int>; Value = std::pair<std::pair<int, int>, int>; Key = std::pair<int,  int>; HashFcn = spp::spp_hash<std::pair<int, int> >; ExtractKey = spp::spar se_hash_map<std::pair<int, int>, int>::SelectKey; SetKey = spp::sparse_hash_ map<std::pair<int, int>, int>::SetKey; EqualKey = std::equal_to<std::pair<in t, int> >; Alloc = spp::libc_allocator_with_realloc<std::pair<const std::pai r<int, int>, int> >; typename spp::sparsetable<Value, typename Alloc::rebind <Value>::other>::ne_iterator = spp::Two_d_iterator<std::pair<std::pair<int,  int>, int>, spp::sparsegroup<std::pair<std::pair<int, int>, int>, spp::libc_ allocator_with_realloc<std::pair<std::pair<int, int>, int> > >*, std::pair<c onst std::pair<int, int>, int>*, std::bidirectional_iterator_tag>]' sparsepp-master/sparsepp.h:4451:36:   required from 'std::pair<typename spp: :sparsetable<Value, typename Alloc::rebind<Value>::other>::ne_iterator, bool > spp::sparse_hashtable<Value, Key, HashFcn, ExtractKey, SetKey, EqualKey, A lloc>::insert(spp::sparse_hashtable<Value, Key, HashFcn, ExtractKey, SetKey,  EqualKey, Alloc>::const_reference) [with Value = std::pair<std::pair<int, i nt>, int>; Key = std::pair<int, int>; HashFcn = spp::spp_hash<std::pair<int,  int> >; ExtractKey = spp::sparse_hash_map<std::pair<int, int>, int>::Select Key; SetKey = spp::sparse_hash_map<std::pair<int, int>, int>::SetKey; EqualK ey = std::equal_to<std::pair<int, int> >; Alloc = spp::libc_allocator_with_r ealloc<std::pair<const std::pair<int, int>, int> >; typename spp::sparsetabl e<Value, typename Alloc::rebind<Value>::other>::ne_iterator = spp::Two_d_ite rator<std::pair<std::pair<int, int>, int>, spp::sparsegroup<std::pair<std::p air<int, int>, int>, spp::libc_allocator_with_realloc<std::pair<std::pair<in t, int>, int> > >*, std::pair<const std::pair<int, int>, int>*, std::bidirec tional_iterator_tag>; spp::sparse_hashtable<Value, Key, HashFcn, ExtractKey,  SetKey, EqualKey, Alloc>::const_reference = const std::pair<const std::pair <int, int>, int>&; spp::sparse_hashtable<Value, Key, HashFcn, ExtractKey, Se tKey, EqualKey, Alloc>::value_type = std::pair<const std::pair<int, int>, in t>]' sparsepp-master/sparsepp.h:5069:77:   required from 'std::pair<typename spp: :sparse_hashtable<std::pair<typename spp::remove_const<Key>::type, T>, Key,  HashFcn, spp::sparse_hash_map<Key, T, HashFcn, EqualKey, Alloc>::SelectKey,  spp::sparse_hash_map<Key, T, HashFcn, EqualKey, Alloc>::SetKey, EqualKey, Al loc>::iterator, bool> spp::sparse_hash_map<Key, T, HashFcn, EqualKey, Alloc> ::insert(const value_type&) [with Key = std::pair<int, int>; T = int; HashFc n = spp::spp_hash<std::pair<int, int> >; EqualKey = std::equal_to<std::pair< int, int> >; Alloc = spp::libc_allocator_with_realloc<std::pair<const std::p air<int, int>, int> >; typename spp::sparse_hashtable<std::pair<typename spp ::remove_const<Key>::type, T>, Key, HashFcn, spp::sparse_hash_map<Key, T, Ha shFcn, EqualKey, Alloc>::SelectKey, spp::sparse_hash_map<Key, T, HashFcn, Eq ualKey, Alloc>::SetKey, EqualKey, Alloc>::iterator = spp::Two_d_iterator<std ::pair<std::pair<int, int>, int>, spp::sparsegroup<std::pair<std::pair<int,  int>, int>, spp::libc_allocator_with_realloc<std::pair<std::pair<int, int>,  int> > >*, std::pair<const std::pair<int, int>, int>*, std::bidirectional_it erator_tag>; spp::sparse_hash_map<Key, T, HashFcn, EqualKey, Alloc>::value_t ype = std::pair<const std::pair<int, int>, int>]' main.cpp:6:49:   required from here sparsepp-master/sparsepp.h:943:27: error: use of deleted function 'std::hash <std::pair<int, int> >::hash()'          SPP_HASH_CLASS<T> hasher;                            ^~~~~~ In file included from E:/mingw-w64/x86_64-6.3.0-posix-seh-rt_v5-rev2/mingw64 /lib/gcc/x86_64-w64-mingw32/6.3.0/include/c++/bits/basic_string.h:5628:0,                  from E:/mingw-w64/x86_64-6.3.0-posix-seh-rt_v5-rev2/mingw64 /lib/gcc/x86_64-w64-mingw32/6.3.0/include/c++/string:52,                  from sparsepp-master/sparsepp.h:839,                  from main.cpp:2: E:/mingw-w64/x86_64-6.3.0-posix-seh-rt_v5-rev2/mingw64/lib/gcc/x86_64-w64-mi ngw32/6.3.0/include/c++/bits/functional_hash.h:85:12: note: 'std::hash<std:: pair<int, int> >::hash()' is implicitly deleted because the default definiti on would be ill-formed:      struct hash : __hash_enum<_Tp>             ^~~~ E:/mingw-w64/x86_64-6.3.0-posix-seh-rt_v5-rev2/mingw64/lib/gcc/x86_64-w64-mi ngw32/6.3.0/include/c++/bits/functional_hash.h:85:12: error: no matching fun ction for call to 'std::__hash_enum<std::pair<int, int>, false>::__hash_enum ()' E:/mingw-w64/x86_64-6.3.0-posix-seh-rt_v5-rev2/mingw64/lib/gcc/x86_64-w64-mi ngw32/6.3.0/include/c++/bits/functional_hash.h:66:7: note: candidate: std::_ _hash_enum<_Tp, <anonymous> >::__hash_enum(std::__hash_enum<_Tp, <anonymous>  >&&) [with _Tp = std::pair<int, int>; bool <anonymous> = false]        __hash_enum(__hash_enum&&);        ^~~~~~~~~~~ E:/mingw-w64/x86_64-6.3.0-posix-seh-rt_v5-rev2/mingw64/lib/gcc/x86_64-w64-mi ngw32/6.3.0/include/c++/bits/functional_hash.h:66:7: note:   candidate expec ts 1 argument, 0 provided E:/mingw-w64/x86_64-6.3.0-posix-seh-rt_v5-rev2/mingw64/lib/gcc/x86_64-w64-mi ngw32/6.3.0/include/c++/bits/functional_hash.h:85:12: error: 'std::__hash_en um<_Tp, <anonymous> >::~__hash_enum() [with _Tp = std::pair<int, int>; bool  <anonymous> = false]' is private within this context      struct hash : __hash_enum<_Tp>             ^~~~ E:/mingw-w64/x86_64-6.3.0-posix-seh-rt_v5-rev2/mingw64/lib/gcc/x86_64-w64-min gw32/6.3.0/include/c++/bits/functional_hash.h:67:7: note: declared private he re        ~__hash_enum();        ^ In file included from main.cpp:2:0: sparsepp-master/sparsepp.h:943:27: error: use of deleted function 'std::hash< std::pair<int, int> >::~hash()'          SPP_HASH_CLASS<T> hasher;                            ^~~~~~ In file included from E:/mingw-w64/x86_64-6.3.0-posix-seh-rt_v5-rev2/mingw64/ lib/gcc/x86_64-w64-mingw32/6.3.0/include/c++/bits/basic_string.h:5628:0,                  from E:/mingw-w64/x86_64-6.3.0-posix-seh-rt_v5-rev2/mingw64/ lib/gcc/x86_64-w64-mingw32/6.3.0/include/c++/string:52,                  from sparsepp-master/sparsepp.h:839,                  from main.cpp:2: E:/mingw-w64/x86_64-6.3.0-posix-seh-rt_v5-rev2/mingw64/lib/gcc/x86_64-w64-min gw32/6.3.0/include/c++/bits/functional_hash.h:85:12: note: 'std::hash<std::pa ir<int, int> >::~hash()' is implicitly deleted because the default definition  would be ill-formed:      struct hash : __hash_enum<_Tp>             ^~~~ E:/mingw-w64/x86_64-6.3.0-posix-seh-rt_v5-rev2/mingw64/lib/gcc/x86_64-w64-min gw32/6.3.0/include/c++/bits/functional_hash.h:85:12: error: 'std::__hash_enum <_Tp, <anonymous> >::~__hash_enum() [with _Tp = std::pair<int, int>; bool <an onymous> = false]' is private within this context E:/mingw-w64/x86_64-6.3.0-posix-seh-rt_v5-rev2/mingw64/lib/gcc/x86_64-w64-min gw32/6.3.0/include/c++/bits/functional_hash.h:67:7: note: declared private he re        ~__hash_enum();        ^ In file included from main.cpp:2:0: sparsepp-master/sparsepp.h:944:22: error: no match for call to '(std::hash<st d::pair<int, int> >) (const std::pair<int, int>&)'          return hasher(__v);                 ~~~~~~^~~~~

C++：”你叼是吧？你调啊？你调啊？怎么不调了？刚才不是很跳么？哎我就不明白了，你现在嘴长哪去了？刚才blablablabla不是很能说嘛？你现在倒是说说看程序错哪里了啊？“
user avatar    网友的相关建议: 
      

假如语言是不同的杂货铺，那应该是这样的：


C语言的杂货铺：

「老板，来个锤子」

「错误，没有找到锤子」


Java的杂货铺：

「老板，来个锤子」

「错误，在工厂中没有找到锤子」


Python的杂货铺

「老板，来个锤子」

「给你把榔头，它能做锤子用」


Haskell的杂货铺

「老板，来个锤子」

「错误，锤子没有定义 Sell 实例」


C++的杂货铺

「老板，来个锤子」

「错误，地球是绕着太阳转的，月亮是绕着地球转的」
user avatar   jiang-yong-hang 网友的相关建议: 
      

C/C++之所以高效，是因为把其他语言交给编译器负责的功能都开放给程序员了，封装程度非常低。

结果就是程序员要负责处理这些本来是编译器处理的事情，但程序员的水平参差不齐，结果就是写出来的代码（主要是编译器的功能）千奇百怪、bug不停、难懂难维护。

也难怪，编译器这种东西，一般都是最顶尖的工程师才能维护的，一般程序员真干不来。

打个比方就是，其他语言的程序员好像是在搬运集装箱，垒出来的是方方正正的形状；而C/C++程序员则是在搬运大小不一、形状不一、硬度不一的快递包裹，自然垒出来的都是一言难尽的异形。如果还需要和其他程序员码出的版本不一的异形连接合并，自然就变成了更大的异形，连接处还是各显神通的技巧。
为什么我时不时会看到「珍惜生命，远离 C++」？ 的其他答案 点击这里
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