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• Using concurrently 2 versions of boost

  - by idimba

  I'm using RHEL 5.3, which is shipped with gcc 4.1.2 and boost 1.33. There're some features I want, that are missing in the boost 1.33. Therefore the thought was to upgrade to fresh boost release 1.43. Is it possible to use concurrently some header-only library(s) from boost 1.43 and the rest from 1.33? For example I want to use unorded_map, which is missing in boost 1.33. Is it possible to use concurrently binary boost libraries from different releases?

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• Why "constructor-way" of declaring variable in "for-loop" allowed but in "if-statement" not allowed?

  - by PiotrNycz

  Consider this simple example: /*1*/ int main() { /*2*/ for (int i(7); i;){break;} /*3*/ if (int i(7)) {} /*4*/ } Why line-2 compiles just fine, whilst line-3 gives the error? This is little strange to me why if-statement is in this aspect treated worse than for-loop? If this is compiler specific - I tested with gcc-4.5.1: prog.cpp: In function 'int main()': prog.cpp:3:7: error: expected primary-expression before 'int' prog.cpp:3:7: error: expected ')' before 'int' I was inspired by this question [UPDATE] I know this compiles just fine: /*1*/ int main() { /*2*/ for (int i = 7; i;){break;} /*3*/ if (int i = 7) {} /*4*/ }

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• Problem with optional arguments in C #defines

  - by imikedaman

  Hi, I'm having a problem with optional arguments in #define statements in C, or more specifically with gcc 4.2: bool func1(bool tmp) { return false; } void func2(bool tmp, bool tmp2) {} #define CALL(func, tmp, ...) func(tmp, ##__VA_ARGS__) int main() { // this compiles CALL(func2, CALL(func1, false), false); // this fails with: Implicit declaration of function 'CALL' CALL(func2, false, CALL(func1, false)); } That's obviously a contrived example, but does show the problem. Does anyone know how I can get the optional arguments to "resolve" correctly? Additional information: If I remove the ## before _VA_ARGS_, and do something like this: bool func2(bool tmp, bool tmp2) { return false; } #define CALL(func, tmp, ...) func(tmp, __VA_ARGS__) int main() { CALL(func2, false, CALL(func2, false, false)); } That compiles, but it no longer works with zero arguments since it would resolve to func(tmp, )

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• Fast comparison of char arrays?

  - by StackedCrooked

  I'm currently working in a codebase where IPv4 addresses are represented as pointers to u_int8. The equality operator is implemented like this: bool Ipv4Address::operator==(const u_int8 * inAddress) const { return (*(u_int32*) this->myBytes == *(u_int32*) inAddress); } This is probably the fasted solution, but it causes the GCC compiler warning: ipv4address.cpp:65: warning: dereferencing type-punned pointer will break strict-aliasing rules How can I rewrite the comparison correctly without breaking strict-aliasing rules and without losing performance points? I have considered using either memcmp or this macro: #define IS_EQUAL(a, b) \ (a[0] == b[0] && a[1] == b[1] && a[2] == b[2] && a[3] == b[3]) I'm thinking that the macro is the fastest solution. What do you recommend?

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• Complete state of a process

  - by sravan

  hi all, I wrote a small program which is as follows: #include<stdio.h> int c=0; int main() { int a=10,b=20; printf("Hello World\n"); c = a+b; printf("%d\n",c); return 0; } I can create a.out file using the command gcc -save-temps helloworld.c. The save-temps flag allows us to save the intermediate files, helloworld.i, helloworld.s, helloworld.o Now i want to know exactly how the stack of this program changes during the execution. Can some one please tell me how to go about it. My aim of this question is to know exactly what all happens during the execution of any program.

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• C pointer initialization and dereferencing, what's wrong here?

  - by randombits

  This should be super simple, but I'm not sure why the compiler is complaining here. #include <stdio.h> #include <stdlib.h> int main(int argc, char *argv[]) { int *n = 5; printf ("n: %d", *n); exit(0); } Getting the following complaints: foo.c: In function ‘main’: foo.c:6: warning: initialization makes pointer from integer without a cast I just want to print the value that the pointer n references. I'm dereferencing it in the printf() statement and I get a segmentation fault. Compiling this with gcc -o foo foo.c.

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• How could my code compliled correctly without necessary headers?

  - by ZhengZhiren

  I use the functions fork(),exec()... But how can this program compiled without including some extra headers(like sys/types.h, sys/wait.h). I use ubuntu 10.04 with gcc version 4.4.3 #include <stdio.h> #include <stdlib.h> int main() { pid_t pid; printf("before fork\n"); pid = fork(); if(pid == 0) { /*child*/ if(execvp("./cpuid", NULL)) { printf("error\n"); exit(0); } } else { if(wait(NULL) != -1) { printf("ok\n"); } } return 0; }

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• Why is this C or C++ macro not expanded by the preprocessor?

  - by Atul

  Can someone points me the problem in the code when compiled with gcc 4.1.0. #define X 10 int main() { double a = 1e-X; return 0; } I am getting error:Exponent has no digits. When i replace X with 10, it works fine. Also i checked with g++ -E command to see the file with preprocessors applied, it has not replaced X with 10. I was under the impression that preprocessor replaces every macro defined in the file with the replacement text with applying any intelligence. Am I wrong? I know this is a really silly question but I am confused and I would rather be silly than confused :). Any comments/suggestions.

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• Is allocating a dynamic array without specifying size well formed code?

  - by Als

  The following simple program snippet gives compilation errorswith gcc-4.3.4. Program: int main() { char *ptr = new char[10]; char *ptr1 = new char[]; return 0; } Compilation errors: prog.cpp: In function ‘int main()’: prog.cpp:4: error: expected primary-expression before ‘]’ token prog.cpp:3: warning: unused variable ‘ptr’ prog.cpp:4: warning: unused variable ‘ptr1’ But the same compiles cleanly with MSVC without any diagnostic message. So my question is: Does the Standard allow an new [] to be called without specifying the size? Or this a bug in MSVC? Can someone provide a reference from the standard which will conclusively say that the above code example is ill-formed or well-formed? I have had a look at: 5.3.4 New [expr.new] & 18.4.1.2 Array forms [lib.new.delete.array] but couldnt find any conclusive evidence about the behavior.

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• Incompatible format types

  - by nebffa

  I'm playing around with strncpy in C and am having some trouble. The code is as follows: #include <stdio.h> #include <string.h> int main(int argc, char *argv[]) { char src[] = "Benjamin Franklin"; char dest[5]; strncpy(src, dest, sizeof(dest) / sizeof(char)); dest[5] = '\0'; printf("%s\n", dest); return 0; } which compiles with no errors using: gcc -Wall -g -Werror test.c -o test and prints out gibberish like p4?? I cannot really understand what I'm doing wrong especially since I have played around with it a lot and been looking online for answers. Perhaps since I am using arrays I am passing the address to printf without realising it?

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• gitk without X11 [closed]

  - by svnpenn

  It has been noted here that Tcl/Tk, and in turn gitk now require X11 under Cygwin. Having run it before and after this change it seems like extreme overkill. I use gitk very lightly, mostly sticking to simply command line git. How could I go about using gitk without X11, perhaps manually installing old version of Tcl/Tk? After some tinkering, I came up with this script that allows gitk without X11 #!/bin/sh # Requires Cygwin packages: git, make, mingw64-i686-gcc-core, wget # Install Tcl wget prdownloads.sf.net/tcl/tcl8.5.12-src.tar.gz tar xf tcl8.5.12-src.tar.gz cd tcl8.5.12/win ./configure --host i686-w64-mingw32 make install cd - # Install Tk wget prdownloads.sf.net/tcl/tk8.5.12-src.tar.gz tar xf tk8.5.12-src.tar.gz cd tk8.5.12/win ./configure --host i686-w64-mingw32 make install cd - # Install gitk cd /usr/local/bin wget raw.github.com/git/git/master/gitk-git/gitk chmod 700 gitk echo 'cygpath -m "$1" | xargs -I% wish85 % -- ${@:3}' > wish cd -

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• Testing for the presence of a character in an string in C

  - by Prab

  What's wrong with this? #include <stdio.h> void main(){ char *s="some text"; printf("%d",is_in(s,'t')); } int is_in(char *s, char c){ while(*s){ if(*s==c) return 1; s++; } return 0; } I get the following compile time error with GCC: test.c:9: error: conflicting types for ‘is_in’ test.c:9: note: an argument type that has a default promotion can’t match an empty parameter name list declaration test.c:5: note: previous implicit declaration of ‘is_in’ was here

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• Why did this code still work?

  - by bstullkid

  Some old code that I just came across: MLIST * new_mlist_link() { MLIST *new_link = (MLIST * ) malloc(sizeof(MLIST)); new_link->next = NULL; new_link->mapi = NULL; new_link->result = 0; } This was being called to build a linked list, however I noticed there is no statement: return new_link; Even without the return statement there, the list still got built properly. Why did this happen? EDT: Platform: Mandriva 2009 64bit Linux 2.6.24.7-server GCC 4.2.3-6mnb1

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• Code compiles etc. but just hangs on run.

  - by Aidan

  Hey guys, My program is meant to parse through a text file, extract relevant data and then save it in a SQL table. I compile it like so.. gcc -o parse parse.c -I/usr/include/mysql -L/usr/lib/mysql -lmysqlclient_r then I run it like so... ./parse > tweets.rss But it just hangs. it doesn't print any printf's I put in to debug. Whats wrong? here is my code... http://pastebin.com/3R45zyMp I'd appreciate any help!

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• printf'ing a matrix

  - by Flavius

  I'm trying to implement an all-purpose function for printing 2D data. What I've come up with is: int mprintf(FILE* f, char* fmt, void** data, size_t cols, size_t rows) The challenge is determining how many bits to read at once from data, based on fmt. The format fmt is going to be the stdlib's-specific format for printf() and alike. Do you have any knowledge of already-existing features from stdlibc (GNU GCC C's) I could use to ease this up? I try avoiding having to do it all manually, because I know "I am stupid" (I don't want to introduce stupid bugs). Thus, reusing code would be the bug-freest way. Thanks Addendum I see there's a /usr/include/printf.h. Can't I use any of those functions to do it right and ease my job at the same time?

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• Logging to screen and to a file

  - by robUK

  What design pattern might apply to logging? What is normally used in this type of situation? Any good tutorials? I am writing a client-server application using C89 and gcc 4.4.4. I now need to implement some logging feature that will display log messages on the screen as well as log to a file. However, I don't want to display all log messages (warning, error, critical, unrecoverable, debug, etc). Maybe I can set so that it will display just errors and nothing else. For example, the user might not be interested in the debug messages on the screen output.

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• C++11: thread_local or array of OpenCL 1.2 cl_kernel objects?

  - by user926918

  I need to run several C++11 threads (GCC 4.7.1) parallely in host. Each of them needs to use a device, say a GPU. As per OpenCL 1.2 spec (p. 357): All OpenCL API calls are thread-safe75 except clSetKernelArg. clSetKernelArg is safe to call from any host thread, and is safe to call re-entrantly so long as concurrent calls operate on different cl_kernel objects. However, the behavior of the cl_kernel object is undefined if clSetKernelArg is called from multiple host threads on the same cl_kernel object at the same time. An elegant way would be to use thread_local cl_kernel objects and the other way I can think of is to use an array of these objects such that i'th thread uses i'th object. As I have not implemented these earlier I was wondering if any of the two are good or are there better ways of getting things done. TIA, S

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• Build multiple sources into multiple targets in a directory

  - by Taschetto

  folks. I'm learning about GNU-Make and I have the following project structure: ~/projects /sysCalls ex1.c ex2.c ex3.c ex4.c ex5.c ex6.c ex7.c Each .c source is very simple, has its own main function and must be built into a corresponding binary (preferably named after its source). But I want to build into a bin directory (added to my .gitignore file). My current Makefile is: CC := gcc CFLAGS := -Wall -g SRC := $(wildcard *.c) TARGET := $(SRC:.c=) all: bin $(TARGET) mv $(TARGET) bin/ bin: mkdir bin clean: rm -fr bin/ It works as expected, but always builds every source. And I don't like moving everything to bin "manually". Any tips or ideas on how this Makefile could be improved?

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• template specilization using member enums

  - by Altan

  struct Bar { enum { Special = 4 }; }; template<class T, int K> struct Foo {}; template<class T> struct Foo<T::Special> {}; Usage: Foo<Bar> aa; fails to compile using gcc 4.1.2 It complains about the usage of T::Special for partial specilization of Foo. If Special was a class the solution would be to a typename in front of it. Is there something equivalent to it for enums (or integers)? Thanks, Altan

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• zeroing out memory

  - by robUK

  Hello, gcc 4.4.4 c89 I am just wondering what most c programmers do when they want to zero out memory. For example I have a buffer of 1024 bytes. Sometimes I do this: char buffer[1024] = {0}; Which will zero all bytes. However, should I declare like this and use memset? char buffer[1024]; . . memset(buffer, 0, sizeof(buffer); Is there any real reason you have to zero the memory? What is the worst that can happen by not doing it? Many thanks for any suggestions,

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• C: stdin and std* errs

  - by user355926

  I want to my manipulate Stdin, then Std* but some errs: $ gcc testFd.c testFd.c:9: error: initializer element is not constant testFd.c:9: warning: data definition has no type or storage class testFd.c:10: error: redefinition of `fd' testFd.c:9: error: `fd' previously defined here testFd.c:10: error: `mode' undeclared here (not in a function) testFd.c:10: error: initializer element is not constant testFd.c:10: warning: data definition has no type or storage class testFd.c:12: error: syntax error before string constant $ cat testFd.c #include <stdio.h> #include <sys/ioctl.h> int STDIN_FILENO = 1; // I want to access typed // Shell commands, dunno about the value: unsigned long F_DUPFD; fd = fcntl(STDIN_FILENO, F_DUPFD, 0); fd = open("/dev/fd/0", mode); printf("STDIN = %s", fd);

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• Operations on 64bit words in 32bit system

  - by Vilo

  I'm new here same as I'm new with assembly. I hope that you can help me to start. I'm using 32bit (i686) Ubuntu to make programs in assembly, using gcc compiler. I know that general-purpose-registers are 32bit (4 bytes) max, but what when I have to operate on 64 bit numbers? Intel's instruction says that higher bits are stored in %edx and lower in %eax Great... So how can I do something with this 2-registers number? I have to convert 64bit dec to bin, then save it to memory and show on the screen. How to make the 64bit quadword at start of the program in .data section?

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• create logging so that the messages will be displayed on screen and logged to a file

  - by robUK

  Hello, gcc 4.4.4 c89 I am writing a client/server application. I have finished and now I want to implement some logging feature that will display log messages on the screen as well as log to a file. However, I don't want to display all log messages (warning, error, critical, unrecoverable, debug, etc). Maybe I can set so that it will display, just errors and debug messages and nothing else. For example, the user might not be interested in the debug messages. Is there any design-pattern that I can follow? What do you normally for for logging? Any tutorials out there that address logging? many thanks for any suggestions,

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• Problem while compiling the code

  - by Atul

  Can someone points me the problem in the code when compiled with gcc 4.1.0. #define X 10 int main() { double a = 1e-X; return 0; } I am getting error:Exponent has no digits. When i replace X with 10, it works fine. Also i checked with g++ -E command to see the file with preprocessors applied, it has not replaced X with 10. I was under the impression that preprocessor replaces every macro defined in the file with the replacement text with applying any intelligence. Am I wrong? I know this is a really silly question but I am confused and I would rather be silly than confused :). Any comments/suggestions.

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• Whats wrong with my makefile

  - by user577220

  ##################################################################### # This is the filesystem makefile "make_BuddyAlloc". # Author:Michael Gomes # Date:2 jan 2011 ###################################################################### #variable defination CC = gcc CFLAGS = -g -O2 SRC_DIR=src INC_DIR=inc OBJ_DIR=obj #List of source files SOURCE= buddyMain.c \ Copy.c \ #List of object files OBJECTS=$(addprefix $(OBJ_DIR)/,$(SOURCE:.c=.o)) #BuddyAlloc is dependent on "obj/*.o". BuddyAlloc : $(OBJECTS) $(CC) $(CFLAGS) -o BuddyAlloc $< #obj/*.o depends on src/*.c and inc/*.h, we are redirecting the object files to obj folder $(OBJECTS):$(SRC_DIR)/$(SOURCE) $(CC) $(CFLAGS) -I$(INC_DIR) -o $(OBJ_DIR)/$(OBJECTS) -c $< #Cleans all the *.exe files clean: rm -f *.exe I have kept the source files under src folder includes under inc folder and the object files are being saved in obj folder .given above is the makefile i am trying to create for my mini project. I keep getting the error no rule to make target 'Copy.c' needed by 'obj/buddyAlloc.o', but it works fine it i dont include Copy.c, what did i do wrong?

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