signedness - Developer IT

Signedness of enum in C/C99/C++/C++x/GNU C/GNU C99

- by osgx

Hello Is enum type signed or unsigned? Is the Signedness of enums differ in C/C99/ANSI C/C++/C++x/GNU C/ GNU C99? Thanks

Worst side effects from chars signedness. (Explanation of signedness effects on chars and casts)

I frequently work with libraries that use char when working with bytes in C++. The alternative is to define a "Byte" as unsigned char but that not the standard they decided to use. I frequently pass bytes from C# into the C++ dlls and cast them to char to work with the library. When casting ints to chars or chars to other simple types what are some of the side effects that can occur. Specifically, when has this broken code that you have worked on and how did you find out it was because of the char signedness? Lucky i haven't run into this in my code, used a char signed casting trick back in an embedded systems class in school. I'm looking to better understand the issue since I feel it is relevant to the work I am doing.

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Array's index and argc signedness

- by tusbar

Hello, The C standard (5.1.2.2.1 Program startup) says: The function called at program startup is named main. [...] It shall be de?ned with a return type of int and with no parameters: int main(void) { /* ... */ } or with two parameters [...] : int main(int argc, char *argv[]) { /* ... */ } And later says: The value of argc shall be nonnegative. Why shouldn't argc be defined as an unsigned int, argc supposedly meaning 'argument count'? Should argc be used as an index for argv? So I started wondering if the C standard says something about the type of array's index. Is it signed? 6.5.2.1 Array subscripting: One of the expressions shall have type ‘‘pointer to object type’’, the other expression shall have integer type, and the result has type ‘‘type’’. It doesn't say anything about its signedness (or I didn't find it). It is pretty common to see codes using negatives array indexes (array[-1]) but isn't it undefined behavior? Should array's indexes be unsigned?

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How to send a Java integer in four bytes to another application?

- by user1468729

public void routeMessage(byte[] data, int mode) { logger.debug(mode); logger.debug(Integer.toBinaryString(mode)); byte[] message = new byte[8]; ByteBuffer byteBuffer = ByteBuffer.allocate(4); ByteArrayOutputStream baoStream = new ByteArrayOutputStream(); DataOutputStream doStream = new DataOutputStream(baoStream); try { doStream.writeInt(mode); } catch (IOException e) { logger.debug("Error converting mode from integer to bytes.", e); return; } byte [] bytes = baoStream.toByteArray(); bytes[0] = (byte)((mode >>> 24) & 0x000000ff); bytes[1] = (byte)((mode >>> 16) & 0x000000ff); bytes[2] = (byte)((mode >>> 8) & 0x00000ff); bytes[3] = (byte)(mode & 0x000000ff); //bytes = byteBuffer.array(); for (byte b : bytes) { logger.debug(b); } for (int i = 0; i < 4; i++) { //byte tmp = (byte)(mode >> (32 - ((i + 1) * 8))); message[i] = bytes[i]; logger.debug("mode, " + i + ": " + Integer.toBinaryString(message[i])); message[i + 4] = data[i]; } broker.routeMessage(message); } I've tried different ways (as you can see from the commented code) to convert the mode to four bytes to send it via a socket to another application. It works well with integers up to 127 and then again with integers over 256. I believe it has something to do with Java types being signed but don't seem to get it to work. Here are some examples of what the program prints. 127 1111111 0 0 0 127 mode, 0: 0 mode, 1: 0 mode, 2: 0 mode, 3: 1111111 128 10000000 0 0 0 -128 mode, 0: 0 mode, 1: 0 mode, 2: 0 mode, 3: 11111111111111111111111110000000 211 11010011 0 0 0 -45 mode, 0: 0 mode, 1: 0 mode, 2: 0 mode, 3: 11111111111111111111111111010011 306 100110010 0 0 1 50 mode, 0: 0 mode, 1: 0 mode, 2: 1 mode, 3: 110010 How is it suddenly possible for a byte to store 32 bits? How could I fix this?

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Can't install egenix-mx-base on Django production VPS

- by Shane

I have been following these instructions for setting up a Django production server with postgres, apache, nginx, and memcache. My problem is that I cannot get egenix-mx-base to install and without this I cannot get psycopg2 to work and therefore no database access :(. I am attempting this on a VPS running a clean install of Ubuntu Hardy (8.04) and have followed all instructions on the site to a T. The error message is as follows: $ easy_install egenix-mx-base Searching for egenix-mx-base Reading http://pypi.python.org/simple/egenix-mx-base/ Reading http://www.egenix.com/products/python/mxBase/ Reading http://www.lemburg.com/python/mxExtensions.html Reading http://www.egenix.com/ Best match: egenix-mx-base 3.1.3 Downloading http://downloads.egenix.com/python/egenix-mx-base-3.1.3.tar.gz Processing egenix-mx-base-3.1.3.tar.gz Running egenix-mx-base-3.1.3/setup.py -q bdist_egg --dist-dir /tmp/easy_install-iF7qzl/egenix-mx-base-3.1.3/egg-dist-tmp-laxvcS Warning: Can't read registry to find the necessary compiler setting Make sure that Python modules _winreg, win32api or win32con are installed. In file included from mx/TextTools/mxTextTools/mxte.c:42: mx/TextTools/mxTextTools/mxte_impl.h: In function ‘mxTextTools_TaggingEngine’: mx/TextTools/mxTextTools/mxte_impl.h:345: warning: pointer targets in initialization differ in signedness mx/TextTools/mxTextTools/mxte_impl.h:364: warning: pointer targets in initialization differ in signedness mx/URL/mxURL/mxURL.c: In function ‘mxURL_SetFromString’: mx/URL/mxURL/mxURL.c:676: warning: pointer targets in initialization differ in signedness mx/UID/mxUID/mxUID.c: In function ‘mxUID_Verify’: mx/UID/mxUID/mxUID.c:333: warning: pointer targets in passing argument 1 of ‘sscanf’ differ in signedness mx/UID/mxUID/mxUID.c: In function ‘mxUID_New’: mx/UID/mxUID/mxUID.c:462: warning: pointer targets in passing argument 1 of ‘mxUID_CRC16’ differ in signedness error: Setup script exited with error: build/bdist.linux-x86_64-py2.5_ucs4/dumb/egenix_mx_base-3.1.3-py2.5.egg-info: Is a directory Thank you to anyone who takes the time to try to help me.

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Raw Audio Conversion

- by Walidix

While, I'm reading gstreamer document I found this: " Audioconvert converts raw audio buffers between various possible formats. It supports integer to float conversion, width/depth conversion, signedness and endianness conversion and channel transformations." I only understand "depth" (bit number per sample) "signedness and endianness" (for data representation) And now, I'm looking for explanations of : "integer to float conversion" "width" "channel transformations" Thanks in advance

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"C variable type sizes are machine dependent." Is it really true? signed & unsigned numbers ;

- by claws

Hello, I've been told that C types are machine dependent. Today I wanted to verify it. void legacyTypes() { /* character types */ char k_char = 'a'; //Signedness --> signed & unsigned signed char k_char_s = 'a'; unsigned char k_char_u = 'a'; /* integer types */ int k_int = 1; /* Same as "signed int" */ //Signedness --> signed & unsigned signed int k_int_s = -2; unsigned int k_int_u = 3; //Size --> short, _____, long, long long short int k_s_int = 4; long int k_l_int = 5; long long int k_ll_int = 6; /* real number types */ float k_float = 7; double k_double = 8; } I compiled it on a 32-Bit machine using minGW C compiler _legacyTypes: pushl %ebp movl %esp, %ebp subl $48, %esp movb $97, -1(%ebp) # char movb $97, -2(%ebp) # signed char movb $97, -3(%ebp) # unsigned char movl $1, -8(%ebp) # int movl $-2, -12(%ebp)# signed int movl $3, -16(%ebp) # unsigned int movw $4, -18(%ebp) # short int movl $5, -24(%ebp) # long int movl $6, -32(%ebp) # long long int movl $0, -28(%ebp) movl $0x40e00000, %eax movl %eax, -36(%ebp) fldl LC2 fstpl -48(%ebp) leave ret I compiled the same code on 64-Bit processor (Intel Core 2 Duo) on GCC (linux) legacyTypes: .LFB2: .cfi_startproc pushq %rbp .cfi_def_cfa_offset 16 movq %rsp, %rbp .cfi_offset 6, -16 .cfi_def_cfa_register 6 movb $97, -1(%rbp) # char movb $97, -2(%rbp) # signed char movb $97, -3(%rbp) # unsigned char movl $1, -12(%rbp) # int movl $-2, -16(%rbp)# signed int movl $3, -20(%rbp) # unsigned int movw $4, -6(%rbp) # short int movq $5, -32(%rbp) # long int movq $6, -40(%rbp) # long long int movl $0x40e00000, %eax movl %eax, -24(%rbp) movabsq $4620693217682128896, %rax movq %rax, -48(%rbp) leave ret Observations char, signed char, unsigned char, int, unsigned int, signed int, short int, unsigned short int, signed short int all occupy same no. of bytes on both 32-Bit & 64-Bit Processor. The only change is in long int & long long int both of these occupy 32-bit on 32-bit machine & 64-bit on 64-bit machine. And also the pointers, which take 32-bit on 32-bit CPU & 64-bit on 64-bit CPU. Questions: I cannot say, what the books say is wrong. But I'm missing something here. What exactly does "Variable types are machine dependent mean?" As you can see, There is no difference between instructions for unsigned & signed numbers. Then how come the range of numbers that can be addressed using both is different? I was reading http://stackoverflow.com/questions/2511246/how-to-maintain-fixed-size-of-c-variable-types-over-different-machines I didn't get the purpose of the question or their answers. What maintaining fixed size? They all are the same. I didn't understand how those answers are going to ensure the same size.

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Why do C# containers and GUI classes use int and not uint for size related members ?

- by smerlin

I usually program in C++, but for school i have to do a project in C#. So i went ahead and coded like i was used to in C++, but was surprised when the compiler complained about code like the following: const uint size = 10; ArrayList myarray = new ArrayList(size); //Arg 1: cannot convert from 'uint' to 'int Ok they expect int as argument type, but why ? I would feel much more comfortable with uint as argument type, because uint fits much better in this case. Why do they use int as argument type pretty much everywhere in the .NET library even if though for many cases negative numbers dont make any sense (since no container nor gui element can have a negative size). If the reason that they used int is, that they didnt expect that the average user cares about signedness, why didnt they add overloads for uint additonally ? Is this just MS not caring about sign correctness or are there cases where negative values make some sense/ carry some information (error code ????) for container/gui widget/... sizes ?

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