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Search found 122 results on 5 pages for 'c99'.

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  • Running multiple sites on a LAMP with secure isolation

    - by David C.
    Hi everybody, I have been administering a few LAMP servers with 2-5 sites on each of them. These are basically owned by the same user/client so there are no security issues except from attacks through vulnerable deamons or scripts. I am builing my own server and would like to start hosting multiple sites. My first concern is... ISOLATION. How can I avoid that a c99 script could deface all the virtual hosts? Also, should I prevent that c99 to be able to write/read the other sites' directories? (It is easy to "cat" a config.php from another site and then get into the mysql database) My server is a VPS with 512M burstable to 1G. Among the free hosting managers, is there any small one which works for my VPS? (which maybe is compatible with the security approach I would like to have) Currently I am not planning to host over 10 sites but I would not accept that a client/hacker could navigate into unwanted directories or, worse, run malicious scripts. FTP management would be fine. I don't want to complicate things with SSH isolation. What is the best practice in this case? Basically, what do hosting companies do to sleep well? :) Thanks very much! David

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  • C question: Padding bits in unsigned integers and bitwise operations (C89)

    - by Anonymous Question Guy
    I have a lot of code that performs bitwise operations on unsigned integers. I wrote my code with the assumption that those operations were on integers of fixed width without any padding bits. For example an array of 32 bit unsigned integers of which all 32 bits available for each integer. I'm looking to make my code more portable and I'm focused on making sure I'm C89 compliant (in this case). One of the issues that I've come across is possible padded integers. Take this extreme example, taken from the GMP manual: However on Cray vector systems it may be noted that short and int are always stored in 8 bytes (and with sizeof indicating that) but use only 32 or 46 bits. The nails feature can account for this, by passing for instance 8*sizeof(int)-INT_BIT. I've also read about this type of padding in other places. I actually read of a post on SO last night (forgive me, I don't have the link and I'm going to cite something similar from memory) where if you have, say, a double with 60 usable bits the other 4 could be used for padding and those padding bits could serve some internal purpose so they cannot be modified. So let's say for example my code is compiled on a platform where an unsigned int type is sized at 4 bytes, each byte being 8 bits, however the most significant 2 bits are padding bits. Would UINT_MAX in that case be 0x3FFFFFFF (1073741823) ? #include <stdio.h> #include <stdlib.h> /* padding bits represented by underscores */ int main( int argc, char **argv ) { unsigned int a = 0x2AAAAAAA; /* __101010101010101010101010101010 */ unsigned int b = 0x15555555; /* __010101010101010101010101010101 */ unsigned int c = a ^ b; /* ?? __111111111111111111111111111111 */ unsigned int d = c << 5; /* ?? __111111111111111111111111100000 */ unsigned int e = d >> 5; /* ?? __000001111111111111111111111111 */ printf( "a: %X\nb: %X\nc: %X\nd: %X\ne: %X\n", a, b, c, d, e ); return 0; } is it safe to XOR two integers with padding bits? wouldn't I XOR whatever the padding bits are? I can't find this behavior covered in C89. furthermore is the c var guaranteed to be 0x3FFFFFFF or if for example the two padding bits were both on in a or b would c be 0xFFFFFFFF ? same question with d and e. am i manipulating the padding bits by shifting? I would expect to see this below, assuming 32 bits with the 2 most significant bits used for padding, but I want to know if something like this is guaranteed: a: 2AAAAAAA b: 15555555 c: 3FFFFFFF d: 3FFFFFE0 e: 01FFFFFF Also are padding bits always the most significant bits or could they be the least significant bits? Thanks guys EDIT 12/19/2010 5PM EST: Christoph has answered my question. Thanks! I had also asked (above) whether padding bits are always the most significant bits. This is cited in the rationale for the C99 standard, and the answer is no. I am playing it safe and assuming the same for C89. Here is specifically what the C99 rationale says for §6.2.6.2 (Representation of Integer Types): Padding bits are user-accessible in an unsigned integer type. For example, suppose a machine uses a pair of 16-bit shorts (each with its own sign bit) to make up a 32-bit int and the sign bit of the lower short is ignored when used in this 32-bit int. Then, as a 32-bit signed int, there is a padding bit (in the middle of the 32 bits) that is ignored in determining the value of the 32-bit signed int. But, if this 32-bit item is treated as a 32-bit unsigned int, then that padding bit is visible to the user’s program. The C committee was told that there is a machine that works this way, and that is one reason that padding bits were added to C99. Footnotes 44 and 45 mention that parity bits might be padding bits. The committee does not know of any machines with user-accessible parity bits within an integer. Therefore, the committee is not aware of any machines that treat parity bits as padding bits. EDIT 12/28/2010 3PM EST: I found an interesting discussion on comp.lang.c from a few months ago. Bitwise Operator Effects on Padding Bits (VelocityReviews reader) Bitwise Operator Effects on Padding Bits (Google Groups alternate link) One point made by Dietmar which I found interesting: Let's note that padding bits are not necessary for the existence of trap representations; combinations of value bits which do not represent a value of the object type would also do.

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  • Review quality of code

    - by magol
    I have been asked to quality review two code bases. I've never done anything like that, and need advice on how to perform it and report it. Background There are two providers of code, one in VB and one in C (ISO 9899:1999 (C99)). These two programs do not work so well together, and of course, the two suppliers blames each other. I will therefore as a independent person review both codes, on a comprehensive level review the quality of the codes to find out where it is most likely that the problem lies. I will not try to find problems, but simply review the quality and how simple it is to manage and understand the code. Edit: I have yet not received much information about what the problem consists of. I've just been told that I will examine the code in terms of quality. Not so much more. I do not know the background to why they took this decision.

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  • Understanding hand written lexers

    - by Cole Johnson
    I am going to make a compiler for C (C99; I own the standards PDF), written in C (go figure) and looking up on how compilers work on Wikipedia has told me a lot. However, after reading up on lexers has confused me. The Wikipedia page states that: the GNU Compiler Collection (gcc) uses hand-written lexers I have tried googling what a hand written lexer and have come up with nothing except for "making a flowchart that describes how it should function", however, isn't that how all software development should be done? So my question is: "What is a hand written lexer?"

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  • C programming in 2011

    - by Duncan Bayne
    Many moons ago I cut C code for a living, primarily while maintaining a POP3 server that supported a wide range of OSs (Linux, *BSD, HPUX, VMS ...). I'm planning to polish the rust off my C skills and learn a bit about language implementation by coding a simple FORTH in C. But I'm wondering how (or whether?) have things changed in the C world since 2000. When I think C, I think ... comp.lang.c ANSI C wherever possible (but C89 as C99 isn't that widely supported) gcc -Wall -ansi -pedantic in lieu of static analysis tools Emacs Ctags Autoconf + make (and see point 2 for VMS, HP-UX etc. goodness) Can anyone who's been writing in C for the past eleven years let me know what (if anything ;-) ) has changed over the years? (In other news, holy crap, I've been doing this for more than a decade).

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  • redeclaration of enumerator

    - by robUK
    Hello, gcc 4.1.2 c99 I have the following enum's in this file ccsmd.h : enum options_e { acm = 0, anm, smd, OPTIONS_LAST_ENTRY, OPTIONS_ENTRY_COUNT = OPTIONS_LAST_ENTRY }; enum function_mode_e { play = 0, record, bridge, MODE_LAST_ENTRY, MODE_ENTRY_COUNT = MODE_LAST_ENTRY }; error: redeclaration of enumerator ‘LAST_ENTRY’ error: previous definition of ‘LAST_ENTRY’ was here error: redeclaration of enumerator ‘ENTRY_COUNT’ error: previous definition of ‘ENTRY_COUNT’ was here I have the LAST_ENTRY so that I can use that as the index of an array. So I like to keep it the same across all enums. Many thanks for any advice,

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  • Replacement for vsscanf on msvc

    - by ext
    Hi, I've run into an issue porting a codebase from linux (gcc) to windows (msvc). It seems like the C99 function vsscanf isn't available and has no obvious replacement. I've read about a solution using the internal function _input_l and linking statically to the crt runtime, but unfortunately I cannot link statically since it would mess with all the plugins (as dlls) being loaded by the application. So is there any replacement or a way to write a wrapper for vsscanf?

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  • Big numbers in C

    - by teehoo
    I need help working with very big numbers. According to Windows calc, the exponent 174^55 = 1.6990597648061509725749329578093e+123. How would I store this using C (c99 standard). int main(){ long long int x = 174^55; //result is 153 printf("%lld\n", x); } For those curious, it is for a school project where we are implementing the RSA cryptographic algorithm, which deals with exponentiating large numbers with large powers for encryption/decryption.

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  • Logical equality in C

    - by andrew cooke
    [It seems odd this doesn't exist, so apologies in advance if it's a duplicate] I want to test for logical equality in C. In other words, I want to know whether two values would be equal if both were converted in the normal way associated with logical expressions. In C99, I think that (bool)a == (bool)b gives what I want. Is that correct? What is the normal way of writing this in traditional C?

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  • link to a different libc file

    - by bobby
    I want to supply the shared libs along with my program rather than using the system's: ldd says my program uses these shared libs: linux-gate.so.1 = (0xf7ef0000)(made by kernel) libc.so.6 = /lib32/libc.so.6 (0xf7d88000)(libc-2.7.so) /lib/ld-linux.so.2 (0xf7ef1000)(ld-2.7.so) I have successfully linked ld-xxx.so by compiling like this: gcc -std=c99 -D_POSIX_C_SOURCE=200112L -O2 -m32 -s -Wl,-dynamic-linker,ld-2.7.so myprogram.c But I have not managed to successfuly link libc-xxx.so. How can I do that ?

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  • Where do I find the current C or C++ standard documents?

    - by christoffer
    For many questions, especially for C-related ones, the answer seems to be found in "the standard". However, where do we find that - online? Googling can sometimes feel futile, again especially for the C standards, since they are drowned in the flood of discussions on programming forums ;) To get this started, since these are the ones I am searching for right now, where are there good online resources for: C89 C99 C++03

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  • gcc check if file is main (#if __BASE_FILE__ == __FILE__)

    - by Marcin Raczkowski
    Hello. In ruby there's very common idiom to check if current file is "main" file: if __FILE__ == $0 # do something here (usually run unit tests) end I'd like to do something similar in C after reading gcc documentation I've figured that it should work like this: #if __FILE__ == __BASE_FILE__ // Do stuff #endif the only problem is after I try this: $ gcc src/bitmap_index.c -std=c99 -lm && ./a.out src/bitmap_index.c:173:1: error: token ""src/bitmap_index.c"" is not valid in preprocessor expressions Am I using #if wrong?

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  • Using macro to check null values

    - by poliron
    My C code contains many functions with pointers to different structs as parameters which shouldn't be NULL pointers. To make my code more readable, I decided to replace this code: if(arg1==NULL || arg2==NULL || arg3==NULL...) { return SOME_ERROR; } With that macro: NULL_CHECK(arg1,arg2,...) How should I write it, if the number of args is unknown and they can point to different structs?(I work in C99)

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  • Flexible array members in C - bad?

    - by Lionel
    I recently read that using flexible array members in C was poor software engineering practice. However, that statement was not backed by any argument. Is this an accepted fact? (Flexible array members are a C feature introduced in C99 whereby one can declare the last element to be an array of unspecified size. For example: ) struct header { size_t len; unsigned char data[]; };

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  • how to install newer GCC version in CentOS 5.7?

    - by gkdsp
    Using CentOS 5.7, how do I install GCC version 4.6? I just installed version 4.4 using # yum install gcc44 but that version still doesn't support variable length arrays from C99 standard. I don't see a newer version than 4.4 when I type: [root@host2 /etc]# yum list gcc\* Excluding Packages in global exclude list Finished Installed Packages gcc.x86_64 4.1.2-51.el5 installed gcc-c++.x86_64 4.1.2-51.el5 installed gcc-gfortran.x86_64 4.1.2-51.el5 installed gcc44.x86_64 4.4.4-13.el5 installed Available Packages gcc-gnat.x86_64 4.1.2-51.el5 system-base gcc-java.x86_64 4.1.2-51.el5 system-base gcc-objc.x86_64 4.1.2-51.el5 system-base gcc-objc++.x86_64 4.1.2-51.el5 system-base gcc44-c++.x86_64 4.4.4-13.el5 system-base gcc44-gfortran.x86_64 4.4.4-13.el5 system-base I wonder if the newer versions of GCC are not available to CentOS because they're deemed not yet reliable/stable enough (?) Can I download gcc-4.5.3.tar.gz from here: http://fileboar.com/gcc/releases/gcc-4.5.3/ but then how to install?

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  • How to install custom c library?

    - by arijit
    I just wanted to add a c library to Ubuntu which was created by Harvard University for cs50 course. They provided instructions for how to install the library which is listed below. Debian, Ubuntu First become root, as with: sudo su - Then install the CS50 Library as follows: apt-get install gcc wget http://mirror.cs50.net/library/c/cs50-library-c-3.1.zip unzip cs50-library-c-3.1.zip rm -f cs50-library-c-3.1.zip cd cs50-library-c-3.1 gcc -c -ggdb -std=c99 cs50.c -o cs50.o ar rcs libcs50.a cs50.o chmod 0644 cs50.h libcs50.a mkdir -p /usr/local/include chmod 0755 /usr/local/include mv -f cs50.h /usr/local/include mkdir -p /usr/local/lib chmod 0755 /usr/local/lib mv -f libcs50.a /usr/local/lib cd .. rm -rf cs50-library-c-3.1 I did exactly as directed. But the compiler reported “Undefined reference to a function”--the function was Get String. So, I searched for a solution and found one. It said to use the -l switch. Now when I compile I use something like: gcc –o hello.c hello –lcs50 (I don’t remember the exact command.) However, I cannot use the make command, which is easier to use. I understand that there is some problem with linking the library. What is a good solution to this problem?

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  • Multiplying char and int together in C

    - by teehoo
    Today I found the following: #include <stdio.h> int main(){ char x = 255; int z = ((int)x)*2; printf("%d\n", z); //prints -2 return 0; } So basically I'm getting an overflow because the size limit is determined by the operands on the right side of the = sign?? Why doesn't casting it to int before multiplying work? In this case I'm using a char and int, but if I use "long" and "long long int" (c99), then I get similar behaviour. Is it generally advised against doing arithmetic with operands of different sizes?

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  • OpenCL: does it play well with OpenMP, can I connect other languages to it, etc.

    - by Cem Karan
    The 1.0 spec for OpenCL just came out a few days ago (Spec is here) and I've just started to read through it. I want to know if it plays well with other high performance multiprocessing APIs like OpenMP (spec) and I want to know what I should learn. So, here are my basic questions: If I am already using OpenMP, will that break OpenCL or vice-versa? Is OpenCL more powerful than OpenMP? Or are they intended to be complementary? Is there a standard way of connecting an OpenCL program to a standard C99 program (or any other language)? What is it? Does anyone know if anyone is writing an OpenCL book? I'm reading the spec, but I've found books to be more helpful.

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  • Using C preprocessor to construct a string literal for scanf?

    - by Brett
    I'm attempting to create an sscanf string literal to aid in buffer overrun prevention in C99. The goal is something like: #define MAX_ARG_LEN 16 char arg[MAX_ARG_LEN] = ""; if (sscanf(arg, "%"(MAX_ARG_LEN-1)"X", &input) > 0) The obvious "manual" solution is something like: #define MAX_ARG_LEN 16 #define MAX_ARG_CHARS "15" char arg[MAX_ARG_LEN] = ""; if (sscanf(arg, "%"MAX_ARG_CHARS"X", &input) > 0) However, I would prefer something to automatically generate "%15X" given a buffer size of 16. This link is almost works for my application: http://stackoverflow.com/questions/240353/convert-a-preprocessor-token-to-a-string but it does not handle the -1. Suggestions?

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  • the problem about different treatment to __VA_ARGS__ when using VS 2008 and GCC

    - by liuliu
    I am trying to identify a problem because of an unusual usage of variadic macros. Here is the hypothetic macro: #define va(c, d, ...) c(d, __VA_ARGS__) #define var(a, b, ...) va(__VA_ARGS__, a, b) var(2, 3, printf, “%d %d %d\n”, 1); For gcc, the preprocessor will output printf("%d %d %d\n", 1, 2, 3) but for VS 2008, the output is printf, “%d %d %d\n”, 1(2, 3); I suspect the difference is caused by the different treatment to VA_ARGS, for gcc, it will first expand the expression to va(printf, "%d %d %d\n", 1, 2, 3), and treat 1, 2, 3 as the VA_ARGS for macro va. But for VS 2008, it will first treat b as VA_ARGS for macro va, and then do the expansion. Which one is correct interpretation for C99 variadic macro? or my usage falls into an undefined behavior?

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  • How to migrate existing udp application to raw sockets

    - by osgx
    Hello Is there a tutorial for migration from plain udp sockets (linux, C99/C++, recv syscall is used) to the raw sockets? According to http://aschauf.landshut.org/fh/linux/udp_vs_raw/ch03s04.html raw socket is much faster than udp. Application is client-server. client is proprietary and must use exactly same procotol as it was with udp server. But server can be a bit faster with raw sockets. What parts of udp I must to implement in server? Is there a "quick migration" libraries?

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  • Can bad stuff happen when dividing 1/a very small float?

    - by Jeremybub
    If I want to check that positive float A is less than the inverse square of another positive float B (in C99), could something go wrong if B is very small? I could imagine checking it like if(A<1/(B*B)) but if B is small enough, would this possibly result in infinity? If that were to happen, would the code still work correctly in all situations? in a similar vein, I might do if(1/A>B*B) Which might be slightly better because B*B might be zero if B is small (is this true?) Finally, a solution that I can't imagine being wrong is if(sqrt(1/A)>B) Which I don't think would ever result in zero division, but still might be problematic if A is close to zero. So basically, my questions are Can 1/X ever be infinity if X is greater than zero (but small)? Can X*X ever be zero if X is greater than zero? Will comparisons with infinity work the way I would expect them to?

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