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  • Using memory mapping in C for reading binary

    - by user1320912
    I am trying to read data from a binary file and process it.It is a very large file so I thought I would use memory mapping. I am trying to use memory mapping so I can read the file byte by byte. I am getting a few compiler errors while doing this. I am doing this on a linux platform #include <unistd.h> #include <sys/types.h> #include <sys/mman.h> int fd; char *data; fd = open("data.bin", O_RDONLY); pagesize = 4000; data = mmap((caddr_t)0, pagesize, PROT_READ, MAP_SHARED, fd, pagesize); The errors i get are : caddr not initialized, R_RDONLY not initialized, mmap has too few arguments. Could someone help me out ?

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  • fopen in C(Linux) returns "Too many open files"

    - by liv2hak
    static char filename[128] = "trace.txt"; g_file = fopen(filename, "w"); if(NULL == g_file) { printf("Cannot open file %s.error %s\n",filename,strerror(errno)); exit(1); } I am trying to open a empty text file named trace.txt in write mode (in my working directory.) The program is creating an empty file trace.txt in my directory.but the check (NULL == g_file) is returning true and it is returning error code 24 (Too many open files.).Any idea why this is.This is the first file I am opening in my program.

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  • Double indirection and structures passed into a function

    - by ZPS
    I am curious why this code works: typedef struct test_struct { int id; } test_struct; void test_func(test_struct ** my_struct) { test_struct my_test_struct; my_test_struct.id=267; *my_struct = &my_test_struct; } int main () { test_struct * main_struct; test_func(&main_struct); printf("%d\n",main_struct->id); } This works, but pointing to the memory address of a functions local variable is a big no-no, right? But if i used a structure pointer and malloc, that would be the correct way, right? void test_func(test_struct ** my_struct) { test_struct *my_test_struct; my_test_struct = malloc(sizeof(test_struct)); my_test_struct->id=267; *my_struct = my_test_struct; } int main () { test_struct * main_struct; test_func(&main_struct); printf("%d\n",main_struct->id); }

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  • How do I use "this" in a member function?

    - by Peter Stewart
    I've written a member function of class Node to read a tree of Nodes in postfix order. It will be called by the Node instance which is the root node of the tree. So: N.postfix(); these appear to be illeagal: *this->left.postfix(); *this->right.postfix(); What is the proper way to do this? class Node { public: const char *cargo; int depth; Node *left; Node *right void Node::postfix() { if (this==__nullptr) { return; } else { *this->left.postfix(); *this->right.postfix(); out<<*this->cargo<<"\n"; return; } };

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  • RSA encrypted data block size

    - by calccrypto
    how do you store an rsa encrypted data block? the output might be significantly greater than the original input data block size, and i dont think people waste memory by padding bucket loads of 0s in front of each data block. besides, how would they be removed? or is each block stored on new lines within the file? if that is the case, how would you tell the difference between legitimate new line and a '\n' char written into the file? what am i missing? im writing the "write to file" part in python, so maybe its one of the differences between: open(file,'w') open(file,'w+b') open(file,'wb') that i dont know. or is it something else?

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  • What's void *userData exactly?

    - by mystify
    In a C function declaration, I have seen this parameter definition: void *userData so, what exactly is that? My guess: the void says it can be anything arbitrary, or even nothing. Almost similar to id of objective-c. It just allows to pass in whatever data structure you like. The star in front of userData says, that the argument must be passed in by reference. So when using this stuff in the function body, typically it must be casted and dereferenced. So if I pass in an pointer to SomeClass instance, I would get that like this: SomeClass *myObj = (SomeClass*)userData; In the case I had nothing special to pass along, I would provide NULL as argument. Are my assumptions correct? Or did I get something wrong?

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  • C++0x, How do I expand a tuple into variadic template function arguments?

    - by Gustaf
    Consider the case of a templated function with variadic template arguments: template<typename Tret, typename... T> Tret func(const T&... t); Now, I have a tuple t of values. How do I call func() using the tuple values as arguments? I've read about the bind() function object, with call() function, and also the apply() function in different some now-obsolete documents. The GNU GCC 4.4 implementation seems to have a call() function in the bind() class, but there is very little documentation on the subject. Some people suggest hand-written recursive hacks, but the true value of variadic template arguments is to be able to use them in cases like above. Does anyone have a solution to is, or hint on where to read about it?

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  • Creating ostream manipulators for a specific class

    - by petersohn
    I have a class that is derived from ostream: class my_ostream: public std::ostream { // ... } I want to make a manipulator (for example do_something), that works specifically to this class, like this: my_ostream s; s << "some text" << do_something << "some more text"; I did the following: std::ostream &do_something(std::ostream &os) { my_ostream *s = dynamic_cast<my_ostream*>(&os); if (s != NULL) { // do something } return os; } This works, but is rather ugly. I tried the following: my_ostream &do_something(my_ostream &s) { // do something return s; } This doesn't work. I also tried another approach: class my_ostream: public std::ostream { // ... my_ostream &operator<<(const do_something & x) { // do something return *this; } } This still doesn't work.

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  • strange results with /fp:fast

    - by martinus
    We have some code that looks like this: inline int calc_something(double x) { if (x > 0.0) { // do something return 1; } else { // do something else return 0; } } Unfortunately, when using the flag /fp:fast, we get calc_something(0)==1 so we are clearly taking the wrong code path. This only happens when we use the method at multiple points in our code with different parameters, so I think there is some fishy optimization going on here from the compiler (Microsoft Visual Studio 2008, SP1). Also, the above problem goes away when we change the interface to inline int calc_something(const double& x) { But I have no idea why this fixes the strange behaviour. Can anyone explane this behaviour? If I cannot understand what's going on we will have to remove the /fp:fastswitch, but this would make our application quite a bit slower.

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  • How to count the letters in a text with Javascript?

    - by Doguhanca
    I am currently trying to write a ''web application'' that has a simple text area inside, in which I want the letters of the text written to be pointed out. For example, if I write: ''How old are you? I am 19 years old'' I need a code to tell me how many 'A's and 'Y's and 'D's (and all letters of the alphabet from 0-26) are used in this sentence when I press a button on a HTML/ CSS page. Could you please tell me what I must write into my .JS file and what I should write into my .HTML file to do this with a click of a button when something is written in the ? I hope my explanation was detailed enough. Thanks! Edit (I'm very sorry for the problems I caused) - What I have done so far looks like this: HTML: <link rel="stylesheet" type="text/css" href="theme.css"> <meta charset="utf-8"> <script src="test.js" type="text/javascript"></script> <div class='header'> Al.Fa.Be </div> <div class='yaz'> <textarea></textarea> </div> <div class='description'> <a href='http://www.google.com'>Ara</a> </div> <div class='description2'> <input id="clickMe" type="button" value="Hesapla" onclick="doFunction();" /> </div> CSS: body{ background:white; } selection{ background:#CCC; } #clickMe{ background:#CCC; border:1px solid #333; } .header{ font-size:70px; font-weight:bold; font-family:Arial; color:#333; margin-left:580px; padding-top:200px; } textarea{ width:1210px; height:40px; color:black; margin-top:20px; margin-left:100px; padding-left:10px; padding-top:10px; font-size:18px; font-family:Arial; } .description{ background:#f2f2f2; padding:6px; width:50px; text-align:center; border:1px solid #ddd; font-family:Arial; margin-left:620px; margin-top:20px; font-size:14px; } .description a{ color:#555; text-decoration:none; } .description2{ background:#f2f2f2; padding:6px; width:60px; text-align:center; border:1px solid #ddd; font-family:Arial; margin-left:750px; margin-top:-30px; font-size:14px; } .description2 a{ color:#555; text-decoration:none; } .yaz{ color:white; } Javascript: // Input name. Count number of alphabets a-z class program                                                          {     public static void main(String[] args)     {         String name = args[0];         int count[] = new int[29];         int i,p;         int n = name.length();         name = name.toUpperCase();         char c;         for (i=0; i<29; i++)         {             count[i] = 0;           }         for (i=0; i<n; i++)         {             c = name.charAt(i);             p = (int) c;             count[p-65]++;         }         for (i=0; i<29 ; i++)         {             if (count[i] >0)             {                 System.out.println((char)(i+65) + " occurs " + count[i] + " times");             }         }     } }

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  • fgets, sscanf, and writing to arrays

    - by alldavidsluck
    beginner question here, I haven't been able to find examples that relate. I'm working on a C program that will take integer input from stdin using fgets and sscanf, and then write it to an array. However, I'm not sure how to make fgets write to the array. #define MAXINT 512 char input[MAXINT] int main(void) { int i; int j; int count=0; int retval; while (1==1) { fgets(input, MAXINT[count], stdin); retval = sscanf(input, "%d", &i); if (retval == 1) { count = count++; } else if (retval != 1) { break; } } Would I simply put fgets in a for loop? or is it more complicated than that?

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  • Compatible types and structures in C

    - by Oli Charlesworth
    I have the following code: int main(void) { struct { int x; } a, b; struct { int x; } c; struct { int x; } *p; b = a; /* OK */ c = a; /* Doesn't work */ p = &a; /* Doesn't work */ return 0; } which fails to compile under GCC (3.4.6), with the following error: test.c:8: error: incompatible types in assignment test.c:9: warning: assignment from incompatible pointer type Now, from what I understand (admittedly from the C99 standard), is that a and c should be compatible types, as they fulfill all the criteria in section 6.2.7, paragraph 1. I've tried compiling with std=c99, to no avail. Presumably my interpretation of the standard is wrong?

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  • Object to Network serialization - with an existing protocol

    - by cpf
    I'm writing a client for a server program written in C++. As is not unusual, all the networking protocol is in a format where packets can be easily memcopied into/out of a C++ structure (1 byte packet code, then different arrangements per packet type). I could do the same thing in C#, but is there an easier way, especially considering lots of the data is fixed-length char arrays that I want to play with as strings? Or should I just suck it up and convert types as needed? I've looked at using the ISerializable interface, but it doesnt look as low level as is required.

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  • Why does a delegate with no parameters compile?

    - by Ryan
    I'm confused why this compiles: private delegate int MyDelegate(int p1, int p2); private void testDelegate() { MyDelegate imp = delegate { return 1; }; } MyDelegate should be a pointer to a method that takes two int parameters and returns another int, right? Why am I allowed to assign a method that takes no parameters? Interestingly, these doesn't compile (it complains about the signature mismatches, as I'd expect) private void testDelegate() { // Missing param MyDelegate imp = delegate(int p1) { return 1; }; // Wrong return type MyDelegate imp2 = delegate(int p1, int p2) { return "String"; }; } Thanks for any help! Ryan

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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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  • Usage of atoi in the c language

    - by maddy
    I don't understand the results of the following C code. main() { char s[] = "AAA"; advanceString(s); } void advanceString(p[3]) { int val = atoi(p); printf("The atoi val is %d\n",val); } Here the atoi val is shown as 0. But I could not figure out the exact reason. As per my understanding, it should be the summation of decimal equivalent of each values in the array.? Please correct me if I am wrong.

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  • assignment vs std::swap and merging and keeping duplicates in seperate object

    - by rubenvb
    Say I have two std::set<std::string>s. The first one, old_options, needs to be merged with additional options, contained in new_options. I can't just use std::merge (well, I do, but not only that) because I also check for doubles and warn the user about this accordingly. To this effect, I have void merge_options( set<string> &old_options, const set<string> &new_options ) { // find duplicates and create merged_options, a stringset containing the merged options // handle duplicated the way I want to // ... old_options = merged_options; } Is it better to use std::swap( merged_options, old_options ); or the assignment I have? Is there a better way to filter duplicates and return the merged set than consecutive calls to std::set_intersection and std::set_union to detect dupes and merge the sets? I know it's slower than one traversal and doing both at once, but these sets are small (performance is not critical) and I trust the Standard more than I trust myself.

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  • What system does before launching iPhone app's main() function?

    - by Eonil
    My app takes too much time to loading. So I put a NSLog in main() function like this to measure loading time from first: int main(int argc, char *argv[]) { NSLog(@"main"); NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; int retVal = UIApplicationMain(argc, argv, nil, nil); [pool release]; return retVal; } But, the log displayed at really later time. Default.png displayed about 5 seconds, all loading process completed in 1~2 seconds after log appeared. What's happening before executing main() function on iPhone app?

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  • C++ conditional compilation

    - by Shaown
    I have the following code snippet #ifdef DO_LOG #define log(p) record(p) #else #define log(p) #endif void record(char *data){ ..... ..... } Now if I call log("hello world") in my code and DO_LOG isn't defined, will the line be compiled, in other words will it eat up the memory for the string "hello world"? P.S. There are a lot of record calls in the program and it is memory sensitive, so is there any other way to conditionally compile so that it only depends on the #define DO_LOG? Thanks in advance.

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  • <function> referenced from; symbol(s) not found.

    - by jfm429
    I have a piece of C code that is used from a C++ function. At the top of my C++ file I have the line: #include "prediction.h" In prediction.h I have this: #ifndef prediction #define prediction #include "structs.h" typedef struct { double estimation; double variance; } response; response runPrediction(int obs, location* positions, double* observations, int targets, location* targetPositions); #endif I also have prediction.c, which has: #include "prediction.h" response runPrediction(int obs, location* positions, double* observations, int targets, location* targetPositions) { // code here } Now, in my C++ file (which as I said includes prediction.h) I call that function, then compile (through Xcode) I get this error: "runPrediction(int, location*, double*, int, location*)", referenced from: mainFrame::respondTo(char*, int)in mainFrame.o ld: symbol(s) not found collect2: ld returned 1 exit status prediction.c is marked for compilation for the current target. I don't have any problems with other .cpp files not being compiled. Any thoughts here?

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  • What is XcvPort (used in OpenPrinter function)

    - by RiskX
    I'm usin the OpenPrinter function and the first parameter the function gets called "pPrinterName" and that's it's MSDN description: [in] Pointer to a null-terminated string that specifies the name of the printer or print server, the printer object, the XcvMonitor, or the XcvPort. For a printer object use: PrinterName,Job xxxx. For an XcvMonitor, use: ServerName,XcvMonitor MonitorName. For an XcvPort, use: ServerName,XcvPort PortName. Obviously I'm interested in the bold part. What exactly is XcvPort? I know it seems like a question of lazy person but I really couldn't find info abou this concept. If I would like to open a printer on port ABC I should write: "\\MySrever,XcvPort ABC"? Thank you for your answers!

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  • incorrect variable value outside main()

    - by cru3l
    i have this code #import <Foundation/Foundation.h> int testint; NSString *teststring; int Test() { NSLog(@"%d",testint); NSLog(@"%@",teststring); } int main (int argc, const char * argv[]) { NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; testint = 5; NSString *teststring = [[NSString alloc] initWithString:@"test string"]; Test(); [pool drain]; return 0; } in output i have: 5 (null) why Test function doesn't see correct teststring value? What should I do, to have correct "test string" in output?

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  • Using .dll methods to load data from file in C# code

    - by Espinas.iss
    I want to use in C# these methods: * int LibRaw::open_datastream(LibRaw_abstract_datastream *stream) * int LibRaw::open_file(const char *rawfile) * int LibRaw::open_buffer(void *buffer, size_t bufsize) * int LibRaw::unpack(void) * int LibRaw::unpack_thumb(void) that are stored in a libraw.dll. These functions one by one load data from file... I've been reading about P/Invoke but i'm not sure how to invoke them. Can anyone show me an example how to use all of these functions together in C# to load file (raw image stored in folder) or just how to PIvoke one of them. Thanx!

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  • parsing/matching string occurrence in C

    - by David
    I have the following string: const char *str = "\"This is just some random text\" 130 28194 \"Some other string\" \"String 3\"" I would like to get the the integer 28194 of course the integer varies, so I can't do strstr("20194"). So I was wondering what would be a good way to get that part of the string? I was thinking to use #include <regex.h> which I already have a procedure to match regexp's but not sure how the regexp in C will look like using the POSIX style notation. [:alpha:]+[:digit:] and if performance will be an issue. Or will it be better using strchr,strstr? Any ideas will be appreciate it

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