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  • Lvalue required error [migrated]

    - by ankur.trapasiya
    While working with pointers i wrote the following code, int main() { int a[]={10,20,30,40,50}; int i; for(i=0;i<5;i++) { printf("\n%d",*a); a++; } return 0; } Now as per my understanding array name itself is an address in c and the pointer arithmetic done is here is correct as per my knowledge. But when i try to run the code it is giving me "Lvalue Required" error. So what is the exact reason for occuring Lvalue required error because before this also i have come across situations where this error is there. Secondly why the arithmetic on the pointer is not legal here in this case?

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  • Button click event in the Ogre3d for ios

    - by user1184398
    Is it possible to access the button click event by using the cursor? These are the steps I followed for the button click event using the SDK trays m_pTrayMgr = new OgreBites::SdkTrayManager("TrayMgr", m_pRenderWnd, m_pMouse, this); I create the buttons m_LeftBtn = tray->createButton(OgreBites:: TL_LEFT, "sdk_button_down", "Left"); m_RightBtn = tray->createButton(OgreBites::TL_RIGHT, "sdk_button_up", "Right"); And I am calling this function void OgreFramework::buttonHit(OgreBites::Button* button) { if(button->getName().compare("sdk_button_down") == 0 ) { printf("XXX"); } } But the button hit function is not getting called... Could somebody provide some sample code? I'm not using any cursor for the click.

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  • how to fix fatal error jvmti.h No such file or directory compilation terminated on c code ubuntu? [on hold]

    - by Blue Rose
    how to fix fatal error jvmti.h No such file or directory compilation terminated c code ubuntu? my c code is: #include "jvmti.h" JNIEXPORT jint JNICALL Agent_OnLoad(JavaVM *jvm, char *options, void *reserved) { /* We return JNI_OK to signify success */ printf("\nBushra Za'areer,\n\n"); return JNI_OK; } JNIEXPORT void JNICALL Agent_OnUnload(JavaVM *vm) { } type this command in terminal: gcc -Wall -W -Werror first_agent.c -o firstagent first_agent.c:1:19: fatal error: jvmti.h: No such file or directory compilation terminated. where java jdk version javac 1.7.0_25 where gcc version gcc version 4.7.3 (Ubuntu/Linaro 4.7.3-2ubuntu4) here should update gcc version to 4.8?

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  • What is the value of a let expression

    - by Grzegorz Slawecki
    From what I understand, every code in f# is an expression, including let binding. Say we got the following code: let a = 5 printfn "%d" a I've read that this would be seen by the compiler as let a = 5 in ( printfn "%d" a ) And so the value of all this would be value of inner expression, which is value of printf. On the other hand, in f# interactive: > let a = 5;; val a : int = 5 Which clearly indicates that the value of let expression is the value bound to the identifier. Q: Can anyone explain what is the value of a let expression? Can it be different in compiled code than in F# interactive?

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  • What is the Big-O time complexity of this algorithm

    - by grebwerd
    I was wondering what the run time of this small program would be? #include <stdio.h> int main(int argc, char* argv[]) { int i; int j; int inputSize; int sum = 0; if(argc == 1) inputSize = 16; else inputSize = atoi(argv[i]); for(i = 1; i <= inputSize; i++){ for(j = i; j < inputSize; j *=2 ){ printf("The value of sum is %d\n",++sum); } } } n S floor(log n - log (n-i)) = ? i =1 and that each summation would be the floor value between log(n) - log(n-i). Would the run time be n log n?

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  • New to Java Programming - Error help

    - by JJJ
    I am going through a Java book and drafting the examples and have run into the following error when compiling this code. Any help would be appreciated thank you. Error: Main.java:3: class Addition is public, should be declared in a file named Addition.java public class Addition        ^ 1 error Code: import java.io.*; import java.util.Scanner; public class Addition {   public static void main(String[] args) { java.util.Scanner input = new java.util.Scanner(System.in);  int number1; int number2; int sum; System.out.print( "Enter first digit: " ); number1 = input.nextInt(); System.out.print( "Enter second digit:" ); number2 = input.nextInt(); sum = number1 + number2; System.out.printf( "Sum is %d\n, sum" );      } }

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  • Best way to get elapsed time in miliseconds in windows

    - by XaitormanX
    I'm trying to do it using two FILETIMEs, casting them to ULONGLONGs, substracting the ULONGLONGs, and dividing the result by 10000. But it's pretty slow, and I want to know if there is a better way to do it.I use c++ with visual studio 2008 express edition. This is what I'm using: FILETIME filetime,filetime2; GetSystemTimeAsFileTime(&filetime); Sleep(100); GetSystemTimeAsFileTime(&filetime2); ULONGLONG time1,time2; time1 = (((ULONGLONG) filetime.dwHighDateTime) << 32) + filetime.dwLowDateTime; time2 = (((ULONGLONG) filetime2.dwHighDateTime) << 32) + filetime2.dwLowDateTime; printf("ELAPSED TIME IN MS:%d",(int)((time2-time1)/10000));

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  • Random List of numbers in C

    - by Ant
    I have just started a C programming course and so far have only done the basics like printf, read a little on variables etc on the course book. The teacher has tasked us with writing a program that will take a value entered by the user, this will be the number of students in the class (25 at the moment but can be variable). It will then list the number of students randomly and place them in 3 columns. The purpose is to sort students into groups of 3 randomly, then display on the screen in columns. Now my question is not for the code that defeats the object of me attempting the exercise, but how to structure it. I can see that using an array can be used to display the list, but really after some pointers on how best to approach the problem in blocks, then I can attempt to program each block.

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  • What is wrong with this code for reading binary files? [on hold]

    - by qed
    What is wrong with this code for reading binary files? It compiles OK, but will not print out the file as planned, in fact, it prints nothing at all. #include <iostream> #include <fstream> int main(int argc, const char *argv[]) { if (argc < 2) { ::std::cerr << "usage: " << argv[0] << " <filename>\n"; return 1; } ::std::basic_ifstream<unsigned char> in(argv[1], ::std::ios::binary); unsigned char uc; while (in.get(uc)) { printf("%02X ", uc); } // TODO: error handling, in case the file could not be opened or read return 0; }

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  • How to write a buffer-overflow exploit in windows XP,x86?

    - by Mask
    void function(int a, int b, int c) { char buffer1[5]; char buffer2[10]; int *ret; ret = buffer1 + 12; (*ret) += 8;//why is it 8?? } void main() { int x; x = 0; function(1,2,3); x = 1; printf("%d\n",x); } The above demo is from here: http://insecure.org/stf/smashstack.html But it's not working here: D:\test>gcc -Wall -Wextra hw.cpp && a.exe hw.cpp: In function `void function(int, int, int)': hw.cpp:6: warning: unused variable 'buffer2' hw.cpp: At global scope: hw.cpp:4: warning: unused parameter 'a' hw.cpp:4: warning: unused parameter 'b' hw.cpp:4: warning: unused parameter 'c' 1 And I don't understand why it's 8 though the author thinks: A little math tells us the distance is 8 bytes. My gdb dump as called: Dump of assembler code for function main: 0x004012ee <main+0>: push %ebp 0x004012ef <main+1>: mov %esp,%ebp 0x004012f1 <main+3>: sub $0x18,%esp 0x004012f4 <main+6>: and $0xfffffff0,%esp 0x004012f7 <main+9>: mov $0x0,%eax 0x004012fc <main+14>: add $0xf,%eax 0x004012ff <main+17>: add $0xf,%eax 0x00401302 <main+20>: shr $0x4,%eax 0x00401305 <main+23>: shl $0x4,%eax 0x00401308 <main+26>: mov %eax,0xfffffff8(%ebp) 0x0040130b <main+29>: mov 0xfffffff8(%ebp),%eax 0x0040130e <main+32>: call 0x401b00 <_alloca> 0x00401313 <main+37>: call 0x4017b0 <__main> 0x00401318 <main+42>: movl $0x0,0xfffffffc(%ebp) 0x0040131f <main+49>: movl $0x3,0x8(%esp) 0x00401327 <main+57>: movl $0x2,0x4(%esp) 0x0040132f <main+65>: movl $0x1,(%esp) 0x00401336 <main+72>: call 0x4012d0 <function> 0x0040133b <main+77>: movl $0x1,0xfffffffc(%ebp) 0x00401342 <main+84>: mov 0xfffffffc(%ebp),%eax 0x00401345 <main+87>: mov %eax,0x4(%esp) 0x00401349 <main+91>: movl $0x403000,(%esp) 0x00401350 <main+98>: call 0x401b60 <printf> 0x00401355 <main+103>: leave 0x00401356 <main+104>: ret 0x00401357 <main+105>: nop 0x00401358 <main+106>: add %al,(%eax) 0x0040135a <main+108>: add %al,(%eax) 0x0040135c <main+110>: add %al,(%eax) 0x0040135e <main+112>: add %al,(%eax) End of assembler dump. Dump of assembler code for function function: 0x004012d0 <function+0>: push %ebp 0x004012d1 <function+1>: mov %esp,%ebp 0x004012d3 <function+3>: sub $0x38,%esp 0x004012d6 <function+6>: lea 0xffffffe8(%ebp),%eax 0x004012d9 <function+9>: add $0xc,%eax 0x004012dc <function+12>: mov %eax,0xffffffd4(%ebp) 0x004012df <function+15>: mov 0xffffffd4(%ebp),%edx 0x004012e2 <function+18>: mov 0xffffffd4(%ebp),%eax 0x004012e5 <function+21>: movzbl (%eax),%eax 0x004012e8 <function+24>: add $0x5,%al 0x004012ea <function+26>: mov %al,(%edx) 0x004012ec <function+28>: leave 0x004012ed <function+29>: ret In my case the distance should be - = 5,right?But it seems not working..

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  • How to write a buffer-overflow exploit in GCC,windows XP,x86?

    - by Mask
    void function(int a, int b, int c) { char buffer1[5]; char buffer2[10]; int *ret; ret = buffer1 + 12; (*ret) += 8;//why is it 8?? } void main() { int x; x = 0; function(1,2,3); x = 1; printf("%d\n",x); } The above demo is from here: http://insecure.org/stf/smashstack.html But it's not working here: D:\test>gcc -Wall -Wextra hw.cpp && a.exe hw.cpp: In function `void function(int, int, int)': hw.cpp:6: warning: unused variable 'buffer2' hw.cpp: At global scope: hw.cpp:4: warning: unused parameter 'a' hw.cpp:4: warning: unused parameter 'b' hw.cpp:4: warning: unused parameter 'c' 1 And I don't understand why it's 8 though the author thinks: A little math tells us the distance is 8 bytes. My gdb dump as called: Dump of assembler code for function main: 0x004012ee <main+0>: push %ebp 0x004012ef <main+1>: mov %esp,%ebp 0x004012f1 <main+3>: sub $0x18,%esp 0x004012f4 <main+6>: and $0xfffffff0,%esp 0x004012f7 <main+9>: mov $0x0,%eax 0x004012fc <main+14>: add $0xf,%eax 0x004012ff <main+17>: add $0xf,%eax 0x00401302 <main+20>: shr $0x4,%eax 0x00401305 <main+23>: shl $0x4,%eax 0x00401308 <main+26>: mov %eax,0xfffffff8(%ebp) 0x0040130b <main+29>: mov 0xfffffff8(%ebp),%eax 0x0040130e <main+32>: call 0x401b00 <_alloca> 0x00401313 <main+37>: call 0x4017b0 <__main> 0x00401318 <main+42>: movl $0x0,0xfffffffc(%ebp) 0x0040131f <main+49>: movl $0x3,0x8(%esp) 0x00401327 <main+57>: movl $0x2,0x4(%esp) 0x0040132f <main+65>: movl $0x1,(%esp) 0x00401336 <main+72>: call 0x4012d0 <function> 0x0040133b <main+77>: movl $0x1,0xfffffffc(%ebp) 0x00401342 <main+84>: mov 0xfffffffc(%ebp),%eax 0x00401345 <main+87>: mov %eax,0x4(%esp) 0x00401349 <main+91>: movl $0x403000,(%esp) 0x00401350 <main+98>: call 0x401b60 <printf> 0x00401355 <main+103>: leave 0x00401356 <main+104>: ret 0x00401357 <main+105>: nop 0x00401358 <main+106>: add %al,(%eax) 0x0040135a <main+108>: add %al,(%eax) 0x0040135c <main+110>: add %al,(%eax) 0x0040135e <main+112>: add %al,(%eax) End of assembler dump. Dump of assembler code for function function: 0x004012d0 <function+0>: push %ebp 0x004012d1 <function+1>: mov %esp,%ebp 0x004012d3 <function+3>: sub $0x38,%esp 0x004012d6 <function+6>: lea 0xffffffe8(%ebp),%eax 0x004012d9 <function+9>: add $0xc,%eax 0x004012dc <function+12>: mov %eax,0xffffffd4(%ebp) 0x004012df <function+15>: mov 0xffffffd4(%ebp),%edx 0x004012e2 <function+18>: mov 0xffffffd4(%ebp),%eax 0x004012e5 <function+21>: movzbl (%eax),%eax 0x004012e8 <function+24>: add $0x5,%al 0x004012ea <function+26>: mov %al,(%edx) 0x004012ec <function+28>: leave 0x004012ed <function+29>: ret In my case the distance should be - = 5,right?But it seems not working.. Why function needs 56 bytes for local variables?( sub $0x38,%esp )

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  • SIMPLE OpenSSL RSA Encryption in C/C++ is causing me headaches

    - by Josh
    Hey guys, I'm having some trouble figuring out how to do this. Basically I just want a client and server to be able to send each other encrypted messages. This is going to be incredibly insecure because I'm trying to figure this all out so I might as well start at the ground floor. So far I've got all the keys working but encryption/decryption is giving me hell. I'll start by saying I am using C++ but most of these functions require C strings so whatever I'm doing may be causing problems. Note that on the client side I receive the following error in regards to decryption. error:04065072:rsa routines:RSA_EAY_PRIVATE_DECRYPT:padding check failed I don't really understand how padding works so I don't know how to fix it. Anywho here are the relevant variables on each side followed by the code. Client: RSA *myKey; // Loaded with private key // The below will hold the decrypted message unsigned char* decrypted = (unsigned char*) malloc(RSA_size(myKey)); /* The below holds the encrypted string received over the network. Originally held in a C-string but C strings never work for me and scare me so I put it in a C++ string */ string encrypted; // The reinterpret_cast line was to get rid of an error message. // Maybe the cause of one of my problems? if(RSA_private_decrypt(sizeof(encrypted.c_str()), reinterpret_cast<const unsigned char*>(encrypted.c_str()), decrypted, myKey, RSA_PKCS1_OAEP_PADDING)==-1) { cout << "Private decryption failed" << endl; ERR_error_string(ERR_peek_last_error(), errBuf); printf("Error: %s\n", errBuf); free(decrypted); exit(1); } Server: RSA *pkey; // Holds the client's public key string key; // Holds a session key I want to encrypt and send //The below will hold the encrypted message unsigned char *encrypted = (unsigned char*)malloc(RSA_size(pkey)); // The reinterpret_cast line was to get rid of an error message. // Maybe the cause of one of my problems? if(RSA_public_encrypt(sizeof(key.c_str()), reinterpret_cast<const unsigned char*>(key.c_str()), encrypted, pkey, RSA_PKCS1_OAEP_PADDING)==-1) { cout << "Public encryption failed" << endl; ERR_error_string(ERR_peek_last_error(), errBuf); printf("Error: %s\n", errBuf); free(encrypted); exit(1); } Let me once again state, in case I didn't before, that I know my code sucks but I'm just trying to establish a framework for understanding this. I'm sorry if this offends you veteran coders. Thanks in advance for any help you guys can provide!

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  • PHP bitwise left shifting 32 spaces problem and bad results with large numbers arithmetic operations

    - by Victor Stanciu
    Hello, I have the following problems: First: I am trying to do a 32-spaces bitwise left shift on a large number, and for some reason the number is always returned as-is. For example: echo(516103988<<32); // echoes 516103988 Because shifting the bits to the left one space is the equivalent of multiplying by 2, i tried multiplying the number by 2^32, and it works, it returns 2216649749795176448. Second: I have to add 9379 to the number from the above point: printf('%0.0f', 2216649749795176448 + 9379); // prints 2216649749795185920 Should print: 2216649749795185827

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  • When to address integer overflow in C

    - by Yktula
    Related question: http://stackoverflow.com/questions/199333/best-way-to-detect-integer-overflow-in-c-c In C code, should integer overflow be addressed whenever integers are added? It seems like pointers and array indexes should be checked at all. When should integer overflow be checked for? When numbers are added in C without type explicitly mentioned, or printed with printf, when will overflow occur? Is there a way to automatically detect when an integer arithmetic overflow?

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  • Nested Functions in C - Best Practices

    - by Justin Ethier
    I just realized a function may be defined inside another function in C: void main(){ int foo(){ return 2; }; printf("%d\n", foo()); } Besides being a neat trick, the useful thing about this is that the inner function is private to the outer function. But... is that a good enough reason to do this in a "real-world" application? What are the best practices for using this syntax?

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  • Creating multiple process and simulation in C via fork()

    - by Yakup OZDEN
    i want to create multiple process groups which will call different functions. i write the code below. firstly i want to get following output ./fork 4 5 I am a child: 1 PID: 22330 I am a child2: 1 PID: 22334 I am a child: 2 PID: 22331 I am a child2: 5 PID: 22338 I am a child: 4 PID: 22333 I am a child: 3 PID: 22332 I am a child2: 2 PID: 22335 I am a child2: 4 PID: 22337 I am a child2: 3 PID: 22336 ' #include <stdio.h> #include <stdlib.h> #include <unistd.h> void forkChildren (int nChildren) { int i; pid_t pid; for (i = 1; i <= nChildren; i++) { pid = fork(); if (pid == -1) { /* error handling here, if needed */ return; } if (pid == 0) { printf("I am a child: %d PID: %d\n",i, getpid()); sleep (5); wait(NULL); return; } } } void forkChildren2 (int nChildren) { int i; pid_t pid; for (i = 1; i <= nChildren; i++) { pid = fork(); if (pid == -1) { /* error handling here, if needed */ return; } if (pid == 0) { printf("I am a child2: %d PID: %d\n",i, getpid()); sleep (2); return; } } } the code gives me the output [ozdeny@hyperion ~]$ ./fork 4 5 I am a child: 1 PID: 22330 I am a child: 2 PID: 22331 I am a child: 3 PID: 22332 I am a child: 4 PID: 22333 I am a child2: 1 PID: 22334 I am a child2: 2 PID: 22335 I am a child2: 4 PID: 22337 I am a child2: 5 PID: 22338 [ozdeny@hyperion ~]$ I am a child2: 3 PID: 22336 I am a child2: 1 PID: 22339 I am a child2: 2 PID: 22340 I am a child2: 3 PID: 22341 I am a child2: 4 PID: 22342 I am a child2: 5 PID: 22343 I am a child2: 1 PID: 22345 I am a child2: 2 PID: 22346 I am a child2: 3 PID: 22347 I am a child2: 1 PID: 22349 I am a child2: 2 PID: 22350 I am a child2: 1 PID: 22344 I am a child2: 2 PID: 22352 I am a child2: 3 PID: 22353 I am a child2: 4 PID: 22354 I am a child2: 5 PID: 22355 I am a child2: 3 PID: 22351 I am a child2: 4 PID: 22356 I am a child2: 5 PID: 22357 I am a child2: 4 PID: 22348 I am a child2: 5 PID: 22358

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  • Seg Fault when using std::string on an embedded Linux platform

    - by Brad
    Hi, I have been working for a couple of days on a problem with my application running on an embedded Arm Linux platform. Unfortunately the platform precludes me from using any of the usual useful tools for finding the exact issue. When the same code is run on the PC running Linux, I get no such error. In the sample below, I can reliably reproduce the problem by uncommenting the string, list or vector lines. Leaving them commented results in the application running to completion. I expect that something is corrupting the heap, but I cannot see what? The program will run for a few seconds before giving a segmentation fault. The code is compiled using a arm-linux cross compiler: arm-linux-g++ -Wall -otest fault.cpp -ldl -lpthread arm-linux-strip test Any ideas greatly appreciated. #include <stdio.h> #include <vector> #include <list> #include <string> using namespace std; ///////////////////////////////////////////////////////////////////////////// class TestSeg { static pthread_mutex_t _logLock; public: TestSeg() { } ~TestSeg() { } static void* TestThread( void *arg ) { int i = 0; while ( i++ < 10000 ) { printf( "%d\n", i ); WriteBad( "Function" ); } pthread_exit( NULL ); } static void WriteBad( const char* sFunction ) { pthread_mutex_lock( &_logLock ); printf( "%s\n", sFunction ); //string sKiller; // <----------------------------------Bad //list<char> killer; // <----------------------------------Bad //vector<char> killer; // <----------------------------------Bad pthread_mutex_unlock( &_logLock ); return; } void RunTest() { int threads = 100; pthread_t _rx_thread[threads]; for ( int i = 0 ; i < threads ; i++ ) { pthread_create( &_rx_thread[i], NULL, TestThread, NULL ); } for ( int i = 0 ; i < threads ; i++ ) { pthread_join( _rx_thread[i], NULL ); } } }; pthread_mutex_t TestSeg::_logLock = PTHREAD_MUTEX_INITIALIZER; int main( int argc, char *argv[] ) { TestSeg seg; seg.RunTest(); pthread_exit( NULL ); }

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  • who free's setvbuf buffer?

    - by Evan Teran
    So I've been digging into how the stdio portion of libc is implemented and I've come across another question. Looking at man setvbuf I see the following: When the first I/O operation occurs on a file, malloc(3) is called, and a buffer is obtained. This makes sense, your program should have a malloc in it for I/O unless you actually use it. My gut reaction to this is that libc will clean up its own mess here. Which I can only assume it does because valgrind reports no memory leaks (they could of course do something dirty and not allocate it via malloc directly... but we'll assume that it literally uses malloc for now). But, you can specify your own buffer too... int main() { char *p = malloc(100); setvbuf(stdio, p, _IOFBF, 100); puts("hello world"); } Oh no, memory leak! valgrind confirms it. So it seems that whenever stdio allocates a buffer on its own, it will get deleted automatically (at the latest on program exit, but perhaps on stream close). But if you specify the buffer explicitly, then you must clean it up yourself. There is a catch though. The man page also says this: You must make sure that the space that buf points to still exists by the time stream is closed, which also happens at program termination. For example, the following is invalid: Now this is getting interesting for the standard streams. How would one properly clean up a manually allocated buffer for them, since they are closed in program termination? I could imagine a "clean this up when I close flag" inside the file struct, but it get hairy because if I read this right doing something like this: setvbuf(stdio, 0, _IOFBF, 100); printf("hello "); setvbuf(stdio, 0, _IOLBF, 100); printf("world\n"); would cause 2 allocations by the standard library because of this sentence: If the argument buf is NULL, only the mode is affected; a new buffer will be allocated on the next read or write operation.

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  • Any software for pattern-matching and -rewriting source code?

    - by Steven A. Lowe
    I have some old software (in a language that's not dead but is dead to me ;-)) that implements a basic pattern-matching and -rewriting system for source code. I am considering resurrecting this code, translating it into a modern language, and open-sourcing the project as a refactoring power-tool. Before I go much further, I want to know if anything like this exists already (my google-fu is fanning air on this tonight). Here's how it works: the pattern-matching part matches source-code patterns spanning multiple lines of code using a template with binding variables, the pattern-rewriting part uses a template to rewrite the matched code, inserting the contents of the bound variables from the matching template matching and rewriting templates are associated (1:1) by a simple (unconditional) rewrite rule the software operates on the abstract syntax tree (AST) of the input application, and outputs a modified AST which can then be regenerated into new source code for example, suppose we find a bunch of while-loops that really should be for-loops. The following template will match the while-loop pattern: Template oldLoopPtrn int @cnt@ = 0; while (@cnt@ < @max@) { … @body@ ++@cnt@; } End_Template while the following template will specify the output rewrite pattern: Template newLoopPtrn for(int @cnt@ = 0; @cnt@ < @max@; @cnt@++) { @body@ } End_Template and a simple rule to associate them Rule oldLoopPtrn --> newLoopPtrn so code that looks like this int i=0; while(i<arrlen) { printf("element %d: %f\n",i,arr[i]); ++i; } gets automatically rewritten to look like this for(int i = 0; i < arrlen; i++) { printf("element %d: %f\n",i,arr[i]); } The closest thing I've seen like this is some of the code-refactoring tools, but they seem to be geared towards interactive rewriting of selected snippets, not wholesale automated changes. I believe that this kind of tool could supercharge refactoring, and would work on multiple languages (even HTML/CSS). I also believe that converting and polishing the code base would be a huge project that I simply cannot do alone in any reasonable amount of time. So, anything like this out there already? If not, any obvious features (besides rewrite-rule conditions) to consider? EDIT: The one feature of this system that I like very much is that the template patterns are fairly obvious and easy to read because they're written in the same language as the target source code, not in some esoteric mutated regex/BNF format.

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  • What is C# equivalent of PHP's mysql_fetch_array function?

    - by Mike Biff
    I am learning C#/ASP.NET and I am wondering what the C# equivalent of the following PHP code is? I know the userid, and I want to fetch the rows from this table into the array of the variable "row", so I then can use it as "row['name']" and "row['email']. $result = mysql_query("SELECT email, name FROM mytable WHERE id=7"); while ($row = mysql_fetch_array($result, MYSQL_ASSOC)) { printf("Email: %s Name: %s", $row["email"], $row["name"]); } Thanks.

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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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  • C Programming - My program is good enough for my assignment but I know its not good

    - by Joe
    Hi there I'm just starting an assignment for uni and it's raised a question for me. I don't understand how to return a string from a function without having a memory leak. char* trim(char* line) { int start = 0; int end = strlen(line) - 1; /* find the start position of the string */ while(isspace(line[start]) != 0) { start++; } //printf("start is %d\n", start); /* find the position end of the string */ while(isspace(line[end]) != 0) { end--; } //printf("end is %d\n", end); /* calculate string length and add 1 for the sentinel */ int len = end - start + 2; /* initialise char array to len and read in characters */ int i; char* trimmed = calloc(sizeof(char), len); for(i = 0; i < (len - 1); i++) { trimmed[i] = line[start + i]; } trimmed[len - 1] = '\0'; return trimmed; } as you can see I am returning a pointer to char which is an array. I found that if I tried to make the 'trimmed' array by something like: char trimmed[len]; then the compiler would throw up a message saying that a constant was expected on this line. I assume this meant that for some reason you can't use variables as the array length when initialising an array, although something tells me that can't be right. So instead I made my array by allocating some memory to a char pointer. I understand that this function is probably waaaaay sub-optimal for what it is trying to do, but what I really want to know is: 1. Can you normally initialise an array using a variable to declare the length like: char trimmed[len]; ? 2. If I had an array that was of that type (char trimmed[]) would it have the same return type as a pointer to char (ie char*). 3. If I make my array by callocing some memory and allocating it to a char pointer, how do I free this memory. It seems to me that once I have returned this array, I can't access it to free it as it is a local variable. Many thanks in advance Joe

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  • Calculating CPU frequency in C with RDTSC always returns 0

    - by Nazgulled
    Hi, The following piece of code was given to us from our instructor so we could measure some algorithms performance: #include <stdio.h> #include <unistd.h> static unsigned cyc_hi = 0, cyc_lo = 0; static void access_counter(unsigned *hi, unsigned *lo) { asm("rdtsc; movl %%edx,%0; movl %%eax,%1" : "=r" (*hi), "=r" (*lo) : /* No input */ : "%edx", "%eax"); } void start_counter() { access_counter(&cyc_hi, &cyc_lo); } double get_counter() { unsigned ncyc_hi, ncyc_lo, hi, lo, borrow; double result; access_counter(&ncyc_hi, &ncyc_lo); lo = ncyc_lo - cyc_lo; borrow = lo > ncyc_lo; hi = ncyc_hi - cyc_hi - borrow; result = (double) hi * (1 << 30) * 4 + lo; return result; } However, I need this code to be portable to machines with different CPU frequencies. For that, I'm trying to calculate the CPU frequency of the machine where the code is being run like this: int main(void) { double c1, c2; start_counter(); c1 = get_counter(); sleep(1); c2 = get_counter(); printf("CPU Frequency: %.1f MHz\n", (c2-c1)/1E6); printf("CPU Frequency: %.1f GHz\n", (c2-c1)/1E9); return 0; } The problem is that the result is always 0 and I can't understand why. I'm running Linux (Arch) as guest on VMware. On a friend's machine (MacBook) it is working to some extent; I mean, the result is bigger than 0 but it's variable because the CPU frequency is not fixed (we tried to fix it but for some reason we are not able to do it). He has a different machine which is running Linux (Ubuntu) as host and it also reports 0. This rules out the problem being on the virtual machine, which I thought it was the issue at first. Any ideas why this is happening and how can I fix it?

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