C Preprocessor output -


this question has answer here:

for gcc -e sample.c -o sample.i following input c program,

 #include <stdio.h>  int main() {    printf("hello world\n");    return 0;  }

the sample.i have following output preceded # symbols , wonder line # means. 

# 1 "sample.c" # 1 "<built-in>" # 1 "<command-line>" # 1 "/usr/include/stdc-predef.h" 1 3 4 # 1 "<command-line>" 2 # 1 "sample.c" # 1 "/usr/include/stdio.h" 1 3 4 # 27 "/usr/include/stdio.h" 3 4 ...

there comments person identify how preprocessor expanded various #include <...> macros , other items.

reading these lines provides equivalent of reading logging messages of preprocessor encounters macros , expands them.

# 1 "sample.c"

start on line 1 of input "sample.c"

# 1 "<built-in>"

process built-in c pre-procssor directive (must implementation detail), presented fake "file".

# 1 "<command-line>"

process command line directive (again implementation detail), presented fake "file".

# 1 "/usr/include/stdc-predef.h" 1 3 4

include (at line 1) stdc-predef.h file, it's start of file, suppress warnings permitted system header files, assure symbols treated c symbols.

# 1 "<command-line>" 2

return command line "fake" file.

# 1 "sample.c"

back in sample.c.

# 1 "/usr/include/stdio.h" 1 3 4

now starting file "stdio.h", suppress permitted system warnings, treat symbols in file c symbols.

# 27 "/usr/include/stdio.h" 3 4

and on...

the documentation here.


Comments

Post a Comment

Popular posts from this blog

Is there a better way to structure post methods in Class Based Views -

i'm using class based views in django , never specify url in ajax calls , omit action parameter in form because know these requests go through post method of class based view. notice view - profile page make many requests depending on user updating on page - post method become convoluted , if/else mess example: def post(self, request, *args, **kwargs): # handle user changing available date if request.post.get('availabledate') != none: self.updateavailabledate(request) return jsonresponse({'result':'success'}) if request.post.get('newprojectname') != none: creative_user = creativeuserprofile.objects.get(id = request.user.id) project = project.create_project(creative_user, request.post['newprojectname']) project.save() return jsonresponse({'projectid': project.id }) if request.post.get('projectimage') != none , request.files['file']: proj...
Read more

performance - Why is XCHG reg, reg a 3 micro-op instruction on modern Intel architectures? -

i'm doing micro-optimization on performance critical part of code , came across sequence of instructions (in at&t syntax): add %rax, %rbx mov %rdx, %rax mov %rbx, %rdx i thought had use case xchg allow me shave instruction , write: add %rbx, %rax xchg %rax, %rdx however, dimay found agner fog's instruction tables , xchg 3 micro-op instruction 2 cycle latency on sandy bridge, ivy bridge, broadwell, haswell , skylake. 3 whole micro-ops , 2 cycles of latency! 3 micro-ops throws off 4-1-1-1 cadence , 2 cycle latency makes worse original in best case since last 2 instructions in original might execute in parallel. now... cpu might breaking instruction micro-ops equivalent to: mov %rax, %tmp mov %rdx, %rax mov %tmp, %rdx where tmp anonymous internal register , suppose last 2 micro-ops run in parallel latency 2 cycles. given register renaming occurs on these micro-architectures, though, doesn't make sense me done way. why wouldn't register renamer ...
Read more

c# - Asp.net web api : redirect unauthorized requst to forbidden page -

im trying redirect unauthorized request forbidden page instead i'm getting forbidden page in response body , how can fix ? here's startup class : app.createperowincontext(storecontext.create); app.createperowincontext<applicationusermanager>(applicationusermanager.create); app.createperowincontext<applicationsigninmanager>(applicationsigninmanager.create); app.usecookieauthentication(new cookieauthenticationoptions { authenticationtype = defaultauthenticationtypes.applicationcookie, expiretimespan = timespan.fromdays(30), }); app.useexternalsignincookie(defaultauthenticationtypes.externalcookie); app.usetwofactorsignincookie(defaultauthenticationtypes.twofactorcookie, timespan.fromminutes(5)); app.usetwofactorrememberbrowsercookie(defaultauthenticationtypes.twofactorrememberbrowsercookie); the method im trying reach : [httpget] [authorize(roles = "admin")] public string getcurrentusername() { return userman...
Read more