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• Why freed struct in C still has data?

  - by kliketa

  When I run this code: #include <stdio.h> typedef struct _Food { char name [128]; } Food; int main (int argc, char **argv) { Food *food; food = (Food*) malloc (sizeof (Food)); snprintf (food->name, 128, "%s", "Corn"); free (food); printf ("%d\n", sizeof *food); printf ("%s\n", food->name); } I still get 128 Corn although I have freed food. Why is this? Is memory really freed?

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• Should I use a global var or call the function every time? C++

  - by extintor

  Im using: bool GetOS(LPTSTR pszOS) { OSVERSIONINFOEX osve; BOOL bOsVersionInfoEx; ZeroMemory(&osve, sizeof(OSVERSIONINFOEX)); osve.dwOSVersionInfoSize = sizeof(OSVERSIONINFOEX); if( !(bOsVersionInfoEx = GetVersionEx ((OSVERSIONINFO *) &osve)) ) return false; TCHAR buf[80]; StringCchPrintf( buf, 80, TEXT("%u.%u.%u.%u"), osve.dwPlatformId, osve.dwMajorVersion, osve.dwMinorVersion, osve.dwBuildNumber); StringCchCat(pszOS, BUFSIZE, buf); return true; } to get the windows version, and I am planning to use pszOS every a few minutes, Should I use pszOS as a global var or call GetOS() every time? What's the best option from a performance point of view.

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• Another dynamic memory allocation bug.

  - by m4design

  I'm trying to allocate memory for a multidimensional array (8 rows, 3 columns). Here's the code for the allocation (I'm sure the error is clear for you) char **ptr = (char **) malloc( sizeof(char) * 8); for (i = 0; i < 3; i++) ptr[i] = (char *) malloc( sizeof(char) * 3); The crash happens when I reference this: ptr[3][0]; Unhandled exception at 0x0135144d in xxxx.exe: 0xC0000005: Access violation writing location 0xabababab. Are there any recommended references/readings for this kind of subject? Thanks.

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• Storing CLLocationCoordinates2D in NSMutableArray

  - by Amarsh

  After some searching, I got the following solution : ref: http://stackoverflow.com/questions/1392909/nsmutablearray-addobject-with-mallocd-struct CLLocationCoordinate2D* new_coordinate = malloc(sizeof(CLLocationCoordinate2D)); new_coordinate->latitude = latitude; new_coordinate->longitude = longitude; [points addObject:[NSData dataWithBytes:(void *)new_coordinate length:sizeof(CLLocationCoordinate2D)]]; free(new_coordinate); And access it as: CLLocationCoordinate2D* c = (CLLocationCoordinate2D*) [[points objectAtIndex:0] bytes]; However, someone claims that there is a memory leak here? Can anyone suggest me where is the leak and how to fix it. Further, is there a better way of storing a list of CLLocationCoordinate2D in NSMutableArray? Please give sample code since I am an Objective C newbie.

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• trying to copy a bitmap into the WMP Renderer -> upside down!

  - by Roey

  Hi All. I'm writing a video DMO decoder and trying to return a bitmap to the WMP renderer for display ... but WMP displays it upside down! This is the code : HBITMAP* hBmp = new HBITMAP(); int result; m_pScrRenderer->CreateFrame(hBmp, &result); ///This returns the HBITMAP handle. BITMAP bmStruct; memset(&bmStruct, 0, sizeof(BITMAP)); GetObject(*hBmp, sizeof(BITMAP), &bmStruct); int size = bmStruct.bmWidthBytes * bmStruct.bmHeight; memcpy(pbOutData, bmStruct.bmBits, size); //PBoutData is WMP's renderer buffer. This produces an upside down image. What should I change in this code? Thank You! Roey.

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• reading a file that doesn't exist

  - by John

  Hi, I have got a small program that prints the contents of files using the system call - read. unsigned char buffer[8]; size_t offset=0; size_t bytes_read; int i; int fd = open(argv[1], O_RDONLY); do{ bytes_read = read(fd, buffer, sizeof(buffer)); printf("0x%06x : ", offset); for(i=0; i<bytes_read; ++i) { printf("%c ", buffer[i]); } printf("\n"); offset = offset + bytes_read; }while(bytes_read == sizeof(buffer)); Now while running I give a file name that doesn't exist. It prints some kind of data mixed with environment variables and a segmentation fault at the end. How is this possible? What is the program printing? Thanks, John

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• setsockopt (sys/socket.h)

  - by lojin

  The prototype for setsockopt is: int setsockopt(int socket, int level, int option_name, const void *option_value, socklen_t option_len); Are the following all correct ? Which are not ? a.) int buffsize = 50000; setsockopt(s, SOL_SOCKET, SO_RCVBUF, (char *)&buffsize, sizeof(buffsize)); b.) int buffsize = 50000; setsockopt(s, SOL_SOCKET, SO_RCVBUF, (void *)&buffsize, sizeof(buffsize)); c.) char *buffsize = "50000"; setsockopt(s, SOL_SOCKET, SO_RCVBUF, buffsize, strlen(buffsize)); d.) setsockopt(s, SOL_SOCKET, SO_RCVBUF, "50000", 5);

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• No-overflow cast on x64

  - by Cheeso

  I have an existing C codebase that works on x86. I'm now compiling it for x64. What I'd like to do is cast a size_t to a DWORD, and throw an exception if there's a loss of data. Q: Is there an idiom for this? Here's why I'm doing this: A bunch of Windows APIs accept DWORDs as arguments, and the code currently assumes sizeof(DWORD)==sizeof(size_t). That assumption holds for x86, but not for x64. So when compiling for x64, passing size_t in place of a DWORD argument, generates a compile-time warning. In virtually all of these cases the actual size is not going to exceed 2^32. But I want to code it defensively and explicitly. This is my first x64 project, so... be gentle.

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• c++ : list(vector) definition with array

  - by Meloun

  I have Class Email, there is parameter "bcc" in her construktor. Its actually list of emails for copies. There is no fixed number of these emails and later i have to have possibility to extend this list. //construktor prototype Email::Email(vector<string> bcc) So i want to use type vector or list for that and function push_back(). How can i make a new instance with bcc emails? I need actually declaration with definition for my list. I've found this definition with iterator for integer type: int myints[] = {16,2,77,29}; Email myEmail(vector<int> (myints, myints + sizeof(myints) / sizeof(int) )); , but its not very user friend and i need it with strings. Is there something like this? Email myEmail(vector<string> ("first","second","third"));

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• Question regarding two dimensional array

  - by Sherwood Hu

  I have some problems using two dimensional array in the code and need some help. static const int PATTERNS[20][4]; static void init_PATTERN() { // problem #1 int (&patterns)[20][4] = const_cast<int[20][4]>(PATTERNS); ... } extern void UsePattern(int a, const int** patterns, int patterns_size); // problem #2 UsePattern(10, PATTERNS, sizeof(PATTERNS)/sizeof(PATTERNS[0])); in the first statement, I need to cast the const off the two dimensional array PATTERNS. The reason for this is that the init function is called only once, and in the remaining code, PATTERNS is strictly read-only. In the second statement, I need to pass PATTERNS array to the int** argument. Direct passing resulted a compile error. Thanks!

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• non blocking TCP-acceptor not reading from socket

  - by Abruzzo Forte e Gentile

  I have the code below implementing a NON-Blocking TCP acceptor. Clients are able to connect without any problem and the writing seems occurring as well, but the acceptor doesn't read anything from the socket and the call to read() blocks indefinitely. Am I using some wrong setting for the acceptor? Kind Regards AFG int main(){ create_programming_socket(); poll_programming_connect(); while(1){ poll_programming_read(); } } int create_programming_socket(){ int cnt = 0; p_listen_socket = socket( AF_INET, SOCK_STREAM, 0 ); if( p_listen_socket < 0 ){ return 1; } int flags = fcntl( p_listen_socket, F_GETFL, 0 ); if( fcntl( p_listen_socket, F_SETFL, flags | O_NONBLOCK ) == -1 ){ return 1; } bzero( (char*)&p_serv_addr, sizeof(p_serv_addr) ); p_serv_addr.sin_family = AF_INET; p_serv_addr.sin_addr.s_addr = INADDR_ANY; p_serv_addr.sin_port = htons( p_port ); if( bind( p_listen_socket, (struct sockaddr*)&p_serv_addr , sizeof(p_serv_addr) ) < 0 ) { return 1; } listen( p_listen_socket, 5 ); return 0; } int poll_programming_connect(){ int retval = 0; static socklen_t p_clilen = sizeof(p_cli_addr); int res = accept( p_listen_socket, (struct sockaddr*)&p_cli_addr, &p_clilen ); if( res > 0 ){ p_conn_socket = res; int flags = fcntl( p_conn_socket, F_GETFL, 0 ); if( fcntl( p_conn_socket, F_SETFL, flags | O_NONBLOCK ) == -1 ){ retval = 1; }else{ p_connected = true; } }else if( res == -1 && ( errno == EWOULDBLOCK || errno == EAGAIN ) ) { //printf( "poll_sock(): accept(c_listen_socket) would block\n"); }else{ retval = 1; } return retval; } int poll_programming_read(){ int retval = 0; bzero( p_buffer, 256 ); int numbytes = read( p_conn_socket, p_buffer, 255 ); if( numbytes > 0 ) { fprintf( stderr, "poll_sock(): read() read %d bytes\n", numbytes ); pkt_struct2_t tx_buf; int fred; int i; } else if( numbytes == -1 && ( errno == EWOULDBLOCK || errno == EAGAIN ) ) { //printf( "poll_sock(): read() would block\n"); } else { close( p_conn_socket ); p_connected = false; retval = 1; } return retval; }

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• parsing Two-dimensional array in c

  - by gitter78

  I'm trying to parse an array that looks like the one below: char *arr[][2] = { { "1", "Purple" }, { "2", "Blue" }, { "22", "Red" }, ... }; I was thinking having a loop as: char *func(char *a){ for(i = 0; i<sizeof(arr)/sizeof(arr[0]);i++){ if(strstr(a,arr[i][0])!=NULL) return arr[i][1]; } } char *out; const char *hello = "this is my 2 string"; out = func(hello); In this case, I'm trying to get the second value based on the first one: Purple, Blue Red, etc.. The question is how would go in parsing this and instead of printing out the value, return the value. UPDATE/FIXED: It has been fixed above. Thanks

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• Initializing and accessing a pointer from an array of pointers

  - by idealistikz

  Suppose I have the following: void **Init(int numElems) { //What is the best way to intialize 'ptrElems' to store an array of void *'s? void **ptrElems = malloc(numElems * sizeof(void *)); return ptrElems; } //What is the best way to return a pointer pointing at the index passed as a parameter? void **GetPtr(void **ptrElems, int index) { void **elem = elems + (index * sizeof(void *)); return elem; } First, what is the best way to intialize 'ptrElems' to store an array of pointers? I use malloc because assigning it to an array will not persist after the end of the function. Second, what is the best way to point to the pointer at the specified index? I tried typecasting the first line of the 'GetPtr' function to ensure proper pointer arithmetic, but I receive the warning, 'initialization from incompatible pointer type'. Is it necessary to typecast?

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• problem in reading output of dd command using pipe

  - by Ummar

  I am developing an application, in which I want to redirect the output (progress information) of dd command to my C++ program, but it is not actually getting the output, here is the code FILE * progressInfo = popen("gzip -dc backup/backup.img.gz | pv -ptrbe -i 2 -s 2339876653 | dd of=/dev/sdb","r"); if(!progressInfo) { return -1; } char buf[1024]; while(fgets(buff, sizeof(buff),progressInfo)!=NULL) { std::cout << buff << endl; } but the problem is the progress information is not received in buff, and the output is continuously printed on terminal, and above program halts on while(fgets(buff, sizeof(buff),progressInfo)!=NULL), and as soon as the dd operation is completed, the very next line to loop block is executed. if anyone has any idea why the output is not returned to buff, and its continuously retuned on terminal?

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• callin' c from lua crashs while reallocating

  - by mkind

  hi folks, i got a crazy error within that for-loop matr=realloc(matr, newmax*sizeof(matr*)); for (i=0; i<newmax; i++){ matr[i]=realloc(matr[i], newmax*sizeof(int)); } matr is a multi-dimension array: int **matr. i need to resize column and row. first line resizes column and the for-loop resizes every row. it worked fine in c. now im working on a library for lua and it crashs here. compilin' works fine as well. but calling from lua crashs with lua: malloc.c:3552: mremap_chunk: Assertion `((size + offset) & (mp_.pagesize-1)) == 0' failed. i have no damn idea since it's working fine using it in c.

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• Syntax error while copying an multidimensional array to another in C

  - by mantuko

  We are programming a ST269 microcontroller which has two IR distance sensors. To calibrate these sensors we made one table for each sensor with the distance we measured and the corresponding value we get from the ADC. Now we want to use one function to approximate the values in between. So we defined two two-dimensional arrays (one for each sensor) as global variables. In our function we then want to copy the one array we want to work with to a working array and approximate our values. So here's the code: ... unsigned int ir_werte_re[][] = { {8,553}, ... {83,133} }; unsigned int ir_werte_li[][] = { {8,566}, ... {83,147} }; ... unsigned int geradenaproximation(unsigned int messwert, unsigned int seite) { unsigned int working_array[16][16]; unsigned int i = 0; if (seite == 0) { for (i = 0; i < sizeof(working_array); i++) { working_array[i][0] = ir_werte_li[i][0]; i++; } } else { for (i = 0; i < sizeof(working_array); i++) { working_array[i][0] = ir_werte_re[i][0]; i++; } } i = 0; unsigned int y1 = 0; unsigned int x1 = 0; ... } This code is in a file called sensor.c. We didn't write anything about our global arrays in the sensor.h should we? The sensor.h of course is included in our main.c and there the function is called. We also tried to copy the arrays via memcpy(working_array, ir_werte_li, sizeof(working_array)); And in every way we do this we get a syntax error near unsigned in the line where we're declaring unsigned int y1 = 0; and I'm pretty sure that there is no syntax error in this line : ) The last time I spend coding in C is a few years away so I'm not sure if the way we try to do this is good. Perhaps we can solve this by using a pointer instead of really copying the array or something. So please help me out I'll appreciate your bits on this.

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• Is there a way to convert code to a string and vice versa in Python?

  - by Dragos Toader

  The original question was: Is there a way to declare macros in Python as they are declared in C: #define OBJWITHSIZE(_x) (sizeof _x)/(sizeof _x[0]) Here's what I'm trying to find out: Is there a way to avoid code duplication in Python? In one part of a program I'm writing, I have a function: def replaceProgramFilesPath(filenameBr): def getProgramFilesPath(): import os return os.environ.get("PROGRAMFILES") + chr(92) return filenameBr.replace("<ProgramFilesPath>",getProgramFilesPath() ) In another part, I've got this code embedded in a string that will later be output to a python file that will itself be run: """ def replaceProgramFilesPath(filenameBr): def getProgramFilesPath(): import os return os.environ.get("PROGRAMFILES") + chr(92) return filenameBr.replace("<ProgramFilesPath>",getProgramFilesPath() ) """ How can I build a "macro" that will avoid this duplication?

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• write 2d array to a file in C (Operating system)

  - by Bobj-C

  Hello All, I used to use the code below to Write an 1D array to a File: FILE *fp; float floatValue[5] = { 1.1F, 2.2F, 3.3F, 4.4F, 5.5F }; int i; if((fp=fopen("test", "wb"))==NULL) { printf("Cannot open file.\n"); } if(fwrite(floatValue, sizeof(float), 5, fp) != 5) printf("File read error."); fclose(fp); /* read the values */ if((fp=fopen("test", "rb"))==NULL) { printf("Cannot open file.\n"); } if(fread(floatValue, sizeof(float), 5, fp) != 5) { if(feof(fp)) printf("Premature end of file."); else printf("File read error."); } fclose(fp); for(i=0; i<5; i++) printf("%f ", floatValue[i]); My question is if i want to write and read 2D array ??

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• Write to a binary file?

  - by rick irby

  Here is data structure w/ variables: struct Part_record { char id_no[3]; int qoh; string desc; double price: }; --- (Using "cin" to input data) --- Part_record null_part = {" ", 0," ",0.0}; --- --- file.seekg( -(long)sizeof(Part_record), ios::cur); file.write( ( char *)&part, sizeof(Part_record) ); The three variables, qoh, Id_no & price, write out correctly, but the "desc" variable is not right. Do I need to initialize Part_record some other way? It should be 20 characters in length. If you have enough info here, pls share your advice,thanks.

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• please help me to find Bug in my Code (segmentation fault)

  - by Vikramaditya Battina

  i am tring to solve this http://www.spoj.com/problems/LEXISORT/ question it working fine in visual studio compiler and IDEone also but when i running in SPOJ compiler it is getting SEGSIGV error Here my code goes #include<stdio.h> #include<stdlib.h> #include<string.h> char *getString(); void lexisort(char **str,int num); void countsort(char **str,int i,int num); int main() { int num_test; int num_strings; char **str; int i,j; scanf("%d",&num_test); for(i=0;i<num_test;i++) { scanf("%d",&num_strings); str=(char **)malloc(sizeof(char *)*num_strings); for(j=0;j<num_strings;j++) { str[j]=(char *)malloc(sizeof(char)*11); scanf("%s",str[j]); } lexisort(str,num_strings); for(j=0;j<num_strings;j++) { printf("%s\n",str[j]); free(str[j]); } free(str); } return 0; } void lexisort(char **str,int num) { int i; for(i=9;i>=0;i--) { countsort(str,i,num); } } void countsort(char **str,int i,int num) { int buff[52]={0,0},k,x; char **temp=(char **)malloc(sizeof(char *)*num); for(k=0;k<52;k++) { buff[k]=0; } for(k=0;k<num;k++) { if(str[k][i]>='A' && str[k][i]<='Z') { buff[(str[k][i]-'A')]++; } else { buff[26+(str[k][i]-'a')]++; } } for(k=1;k<52;k++) { buff[k]=buff[k]+buff[k-1]; } for(k=num-1;k>=0;k--) { if(str[k][i]>='A' && str[k][i]<='Z') { x=buff[(str[k][i]-'A')]; temp[x-1]=str[k]; buff[(str[k][i]-'A')]--; } else { x=buff[26+(str[k][i]-'a')]; temp[x-1]=str[k]; buff[26+(str[k][i]-'a')]--; } } for(k=0;k<num;k++) { str[k]=temp[k]; } free(temp); }

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• In C, is it possible do free only an array first or last position?

  - by user354959

  Hi there! I've an array, but I don't need its first (or last) position. So I point a new variable to the rest of the array, but I should free the array first/last position. For instance: p = read_csv_file(); q = p + 1; // I don't need the first CSV file field // Here I'd like to free only the first position of p return q; Otherwise I've to memcpy the array to other variable, excluding the first position, and then free the original array. Like this: p = read_csv_file(); q = (int*) malloc(sizeof(int) * (SOME_SIZE - 1)); memcpy(q, p+1, sizeof(int) * (SOME_SIZE - 1)); free(p); return q; But then I'll have the overhead of copying all the array. Is this possible to only free a single position of an array?

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• When do I need to deallocate memory? C++

  - by extintor

  I am using this code inside a class to make a webbrowser control visit a website: void myClass::visitWeb(const char *url) { WCHAR buffer[MAX_LEN]; ZeroMemory(buffer, sizeof(buffer)); MultiByteToWideChar(CP_ACP, MB_ERR_INVALID_CHARS, url, strlen(url), buffer, sizeof(buffer)-1); VARIANT vURL; vURL.vt = VT_BSTR; vURL.bstrVal = SysAllocString(buffer); // webbrowser navigate code... VariantClear(&vURL); } Do I need to do some memory deallocation here?, I see vURL is being deallocated by VariantClear but should I deallocate memory for buffer? I've been told that in another bool I have in the same app I shouldn't deallocate anything because everything clear out when the bool return true/false, but what happens on this void?

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• EXC_BAD_ACCESS from AudioBuffer

  - by jfalexvijay

  I am trying to do the record using AudioUnit for iPhone app. Changes: (start) I have added the following code bufferList = (AudioBufferList *)malloc(sizeof(AudioBuffer)); bufferList-mNumberBuffers = 1; bufferList-mBuffers[0].mNumberChannels = 2; bufferList-mBuffers[0].mDataByteSize = 1024; bufferList-mBuffers[0].mData = calloc(256, sizeof(uint32_t)); Changes: (end) static OSStatus recordingCallback(void *inRefCon, AudioUnitRenderActionFlags *ioActionFlags, const AudioTimeStamp *inTimeStamp, UInt32 inBusNumber, UInt32 inNumberFrames, AudioBufferList *ioData) { OSStatus status; status = AudioUnitRender(appdelegate-audioUnit, ioActionFlags, inTimeStamp, inBusNumber, inNumberFrames, appdelegate-bufferList); if(status != 0) NSLog(@"AudioUnitRender status is %d", status); SInt16* samples = (SInt16*)(ioData-mBuffers[0].mData); ..... } fixed: (I am getting OSStatus -50 error code)- Because I didn't initialize the bufferList. I am EXC_BAD_ACCESS from AudioBuffer (ioData-mBuffers[0].mData). I am not sure with this error. Please help me to resolve it.

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• C String input confusion

  - by ahref

  C really isn't my strong point and after reading 3 chapters of a book on the subject and spending ages trying to get stuff working it just doesn't: #include <stdio.h> char *a,*b; int main( ) { char input[10]; fgets(input,sizeof input, stdin); a = input; fgets(input,sizeof input, stdin); b = input; printf("%s : %s",a,b); } I've isolated the problem from my main project. This code is meant to read in two strings and then print them however it seems to be setting a and b to point to input. Sample output from this code when A and B are entered is(don't worry about the \n's i can remove them): A B B : B How do i store the value of input in another variable eg. a or b so that in the above case A B A : B Is output? Thanks

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• Why can't a bind linux service to the loop-back only?

  - by Jon Trauntvein

  I am writing a server application that will provide a service on an ephemeral port that I only want accessible on the loopback interface. In order to do this, I am writing code like the following: struct sockaddr_in bind_addr; memset(&bind_addr,0,sizeof(bind_addr)); bind_addr.sin_family = AF_INET; bind_addr.sin_port = 0; bind_addr.sin_addr.s_addr = htonl(inet_addr("127.0.0.1")); rcd = ::bind( socket_handle, reinterpret_cast<struct sockaddr *>(&bind_addr), sizeof(bind_addr)); The return value for this call to bind() is -1 and the value of errno is 99 (Cannot assign requested address). Is this failing because inet_addr() already returns its result in network order or is there some other reason?

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