Analysis of the template mechanism of C + + compiler function--the essence of function template

Think: Why function templates can be put together with function overloading. How does the C + + compiler provide a mechanism for function templates?

Demo 1

#include <cstdio> #include <iostream>using namespace std;//1.cpp//g++-S 1.cpp-  o 1.stemplate < TypeName T>void Myswap (t &a, t &b) {T c = 0;c = A;a = B;b = c;cout << "Hello ...." I am a template function welcome calll me "<< Endl;} int main () {{int x = ten; int y = 20;myswap<int> (x, y);//1 function template display type call printf ("x:%d y:%d \ n", x, y);} {Char a = ' a '; char b = ' B ';myswap<char> (A, b);//1 function template display type call printf ("a:%c b:%c \ n", A, b);} return 0;}

Compile the demo 1 into a compilation file to view:

. File "1.cpp". Lcomm __zstl8__ioinit,1,1.def___main;. SCl2;. Type32;. Endef.section. Rdata, "Dr" Lc0:.ascii "x:%d y:%d \12\0" Lc1:.ascii "a:%c b:%c \12\0". def___gxx_personality_sj0;. SCl2;. Type32;. Endef.def__unwind_sjlj_register;. SCl2;. Type32;. Endef.def__unwind_sjlj_unregister;. SCl2;. Type32;. Endef.text.globl_main.def_main;. SCl2;. Type32;. Endef_main:pushl%ebpmovl%esp,%ebppushl%edipushl%esipushl%ebxandl$-16,%espsubl$96,%espmovl$___gxx_personality_ Sj0,%esp movl$llsda959, (%ESP) leal60 (%ESP),%EAXMOVL%EBP, (%eax) Movl$l5,%edxmovl%edx, 4 (%EAX) Movl%esp, 8 (%EAX) Leal28 (%ESP),%eaxmovl%eax, (%ESP) call__unwind_sjlj_registercall___mainmovl$10, (%ESP) movl$20, (%ESP) leal88 (% ESP),%eaxmovl%eax, 4 (%ESP) leal92 (%ESP),%eaxmovl%eax, (%ESP) movl$1, (%ESP) <span style= "color: #ff0000;" >call__z6myswapiievrt_s1_//117</span>movl88 (%ESP),%edxmovl92 (%ESP),%eaxmovl%edx, 8 (%ESP) movl%eax , 4 (%ESP) movl$lc0, (%ESP) call_printfmovb$97, (%ESP) movb$98, (%ESP) leal86 (%ESP),%eaxmovl%eax, 4 (%esp) leal87 (%ESP),%eaxmovl%eax, (%ESP) movl$2, (%ESP) <span style= "color: #ff0000;" >call__z6myswapicevrt_s1_//145</span>movb86 (%ESP),%almovsbl%al,%edxmovb87 (%ESP),%almovsbl%al,% Eaxmovl%edx, 8 (%ESP) Movl%eax, 4 (%ESP) Movl$lc1, (%ESP) call_printfmovl$0,%eaxmovl%eax, (%ESP) jmpl8l5:movl36 (%ESP), %edxmovl32 (%ESP),%eaxtestl%eax,%eaxjel6cmpl$1,%eaxjel7.word0x0b0fl6:movl%edx,%eaxmovl%eax, (%ESP) movl$-1, 32 (% ESP) Call__unwind_sjlj_resumel7:movl%edx,%eaxmovl%eax, (%ESP) movl$-1, (%ESP) call__unwind_sjlj_resumel8:leal28 (% ESP),%eaxmovl%eax, (%ESP) call__unwind_sjlj_unregistermovl24 (%ESP),%eaxleal-12 (%EBP),%esppopl%ebxpopl%esipopl% Edipopl%ebpret.section.gcc_except_table, "W" llsda959:.byte0xff.byte0xff.byte0x1.uleb128 llsdacse959-llsdacsb959llsdacsb959:.uleb128 0.uleb128 0.uleb128 0x1.uleb128 0llsdacse959:.text.section. rdata, "Dr". Align 4lc2:.ascii "hello ... \316\322\312\307\304\243\260\345\272\257\312\375 \273\266\323\255 calll \316\322\0". section.text$_z6myswapiievrt_s1_, "x". Linkonce discard.globl__Z6myswapIiEvRT_S1_.def__Z6myswapIiEvRT_S1_;. SCl2;. Type32;. Endef<span style= "color: #ff0000;" >__z6myswapiievrt_s1_://117</span>pushl%ebpmovl%esp,%ebpsubl$40,%espmovl$0, -12 (%EBP) Movl8 (%EBP),% EAXMOVL (%eax),%eaxmovl%eax, -12 (%EBP) movl12 (%EBP),%EAXMOVL (%eax),%edxmovl8 (%EBP),%eaxmovl%edx, (%eax) movl12 (%EBP ),%eaxmovl-12 (%EBP),%edxmovl%edx, (%eax) MOVL$LC2, 4 (%ESP) Movl$__zst4cout, (%ESP) call__zstlsist11char_ Traitsiceerst13basic_ostreamict_es5_pkcmovl$__zst4endlicst11char_traitsiceerst13basic_ostreamit_t0_es6_, (%ESP) Movl%eax,%ecxcall__znsolsepfrsos_esubl$4,%espleaveret.section.text$_z6myswapicevrt_s1_, "X". linkonce discard.globl__Z6myswapIcEvRT_S1_.def__Z6myswapIcEvRT_S1_;. SCl2;. Type32;. Endef<span style= "color: #ff0000;" >__z6myswapicevrt_s1_://145</span>pushl%ebpmovl%esp,%ebpsubl$40,%espmovb$0, -9 (%EBP) Movl8 (%EBP),% Eaxmovb (%eax),%almovb%al, -9 (%EBP) movl12 (%EBP),%eaxmovb (%eax),%dlmovl8 (%EBP),%EAXMOVB%DL, (%eax) movl12 (%EBP),%eaxmovb-9 (%EBP),%DLMOVB%DL, (%eax) MOVL$LC2, 4 (%ESP) Movl$__zst4cout, (%ESP) call__zstlsist11char_ Traitsiceerst13basic_ostreamict_es5_pkcmovl$__zst4endlicst11char_traitsiceerst13basic_ostreamit_t0_es6_, (%ESP) Movl%eax,%ecxcall__znsolsepfrsos_esubl$4,%espleaveret.text.def___tcf_0; Scl3;. Type32;. Endef___tcf_0:pushl%ebpmovl%esp,%ebpsubl$8,%espmovl$__zstl8__ioinit,%ecxcall__znst8ios_ BASE4INITD1EVLEAVERET.DEF__Z41__STATIC_INITIALIZATION_AND_DESTRUCTION_0II;. Scl3;. Type32;. Endef__z41__static_initialization_and_destruction_0ii:pushl%ebpmovl%esp,%ebpsubl$24,%espcmpl$1, 8 (%EBP) jnel12cmpl$65535, (%EBP) Jnel12movl$__zstl8__ioinit,%ecxcall__znst8ios_base4initc1evmovl$___tcf_0, (%ESP) Call_ AtexitL12:leaveret.def__GLOBAL__sub_I_main;. Scl3;. Type32;. Endef__global__sub_i_main:pushl%ebpmovl%esp,%ebpsubl$24,%espmovl$65535, 4 (%ESP) movl$1, (%ESP) call__Z41__static_ Initialization_and_destruction_0iileaveret.section.ctors, "W". Align 4.long__global__sub_i_main.def__unwind_sjlj_ Resume;. SCl2;. Type32;. Endef.def_printf;. SCl2;. Type32;. endef.def__zst4endlicst11char_traitsiceerst13basic_ostreamit_t0_es6_;. SCl2;. Type32;. ENDEF.DEF__ZSTLSIST11CHAR_TRAITSICEERST13BASIC_OSTREAMICT_ES5_PKC;. SCl2;. Type32;. Endef.def__znsolsepfrsos_e;. SCl2;. Type32;. Endef.def__znst8ios_base4initd1ev;. SCl2;. Type32;. Endef.def__znst8ios_base4initc1ev;. SCl2;. Type32;. Endef.def_atexit;. SCl2;. Type32;. Endef

Observation found a phenomenon, the Myswap function template has a declaration, two definitions, this situation and I in the "why there is a function template" mentioned in the two Myswap function is very similar, the actual embodiment of the C + + implementation function template, it would need programmers to write a lot of logic the same, Parameters are different functions, but the C + + compiler helps us do this, according to the call will automatically generate these functions, which is why the function template can be put together with normal functions.

Summary: function template Mechanism conclusion:

The compiler does not process the function template into functions that can handle any class;

The compiler produces different functions from the function template through the specific type;

The compiler compiles the function template two times: compile the template code itself where it is declared, and compile the replacement code at the point where it is called.

Copyright NOTICE: This article for Bo Master original article, without Bo Master permission not reproduced.

Analysis of the template mechanism of C + + compiler function--the essence of function template