I wrote this code to generate a sequence of random number but this program give me the same random number:
int _tmain(int argc, _TCHAR* argv[])
{
for (int i=0;i<100;i++){
srand((unsigned)time(0));
cout<<"\t"<<rand();
}
getchar();
return 0;
}
the output is a sequence with equal number how i can solve this problem.
Only call srand() once, outside the loop, before using rand(). Try:
int _tmain(int argc, _TCHAR* argv[])
{
srand((unsigned)time(0)); // Only call once.
for (int i=0;i<100;i++)
{
cout<<"\t"<<rand();
}
getchar();
return 0;
}
Related
The old code is as below:
char** wargv = new char*[argc];//memory leak!
for(int k = 0; k < argc; ++k)
{
wargv[k] = new char[strlen(argv[k]) + 1];
strncpy(wargv[k], argv[k], strlen(argv[k]));
wargv[k][strlen(argv[k])] = '\0';
}
because there may cause memory leak, so I want to convert wargv to unique_ptr. How to make it?
I know how to convert char* to unique_ptr, the code below works:
int size_t = 10;
std::unique_ptr<char[]> wargv(new char[size_t]{0});
strncpy(wargv.get(), "abcdef", size_t);
but I don't know how to convert char ** to unique_ptr, I tried vector,but it doesn't work.
As #Some programmer dude commented, std::vector<std::string> should be a better choice than std::unique_ptr<>, with memory allocation management.
I try to write a simple example and it works well.
#include <iostream>
#include <string>
#include <vector>
int main(int argc, char** argv) {
std::vector<std::string> collection(argc);
for (auto i = 0; i < argc; i++) {
collection[i] = argv[i];
}
for (const auto& arg : collection) {
std::cout << arg << "\n";
}
}
Using VS2013, in the C++ code below I get a debug assertion when accessing the vector with an out of range index, which is OK (but the catch block is not reached). When running the release version the program runs without the exception being caught. The output is 1 while it should be 0.
#include <iostream>
#include <vector>
#include <stdexcept>
using namespace std;
vector<int> Vector;
void GetException()
try{
int Sum{ 0 };
// Access an element beyond the end of the vector
for( int i = 0; i <= Vector.size(); i++ )
Sum += Vector[i];
}
catch( ... ){
Vector.clear();
}
int _tmain(int argc, _TCHAR* argv[])
{
Vector.push_back( 1 );
GetException();
cout << Vector.size() << endl;
return 0;
}
When I change it to access a nullptr I get in the debug version an error message for an "unhandled exception" and in the release version it crashes on the access. Are there parameters in VS that modify the behaviour of exceptions?
int Sum{ 0 };
void GetException()
try{
int *pSum{ nullptr };
Sum = *pSum;
}
catch( ... ){
Sum = 1;
}
int _tmain(int argc, _TCHAR* argv[])
{
GetException();
cout << Sum << endl;
return 0;
}
This expression Vector[i] (in your first code example) does not throw exceptions (in normal, release builds anyways), it's simply undefined behavior if i is out of bounds.
This expression Vector.at(i) does throw exceptions (in normal, release builds) if i is out of bounds.
If you want to have a std::vector do bounds checking for you, and throw exceptions if an access is out of bounds, then you should use that form. You can't catch the problem if a Vector[i] access is out of bounds.
I am trying to put the values from the vector into the int.
Given vector :'1','0','1','1','1','0','1','1','1','0','1','1','1','0','1','1' :
Expected output (binary representation for the variable out):
00000000000000001011101110111011.
However, I am getting the following output:
10111011101110110000000000000000
Notice: the insertion begun at the 16bit from right end instead of beginning from the leftmost bit
#include<vector>
#include<iostream>
int main() {
std::vector<unsigned char> test = {'1','0','1','1','1','0','1','1','1','0','1','1','1','0','1','1'};
std::vector<unsigned int> out(1);
int j = 0;
for (int i =0; i < test.size(); i++) {
out[j] = out[j] << 1;
if (test[i] == '1') {out[j] |=0x1;}
}
j++;
for (int p = 0; p < j; p++) {
for (int k = 0; k<32; k++ ) {
std::cout << !!((out[p]<<k)&0x8000);
}
std::cout << std::endl;
}
std::cout << "Size Of:" << sizeof(int);
return 0;
}
The reason why this happens is that you are using a wrong constant for the mask: 0x8000 has its 16-bit set, while you probably meant to use 0x80000000 with the 32-nd bit set. To avoid mistakes like that it's best to construct masks with shifts, for example
(1 << 31)
This expression is evaluated at compile time, so the result is the same as if you computed the constant yourself.
Note that both 0x8000 and 0x80000000 constants are system-dependent. Moreover, 0x80000000 assumes 32-bit int, which is not guaranteed.
A better approach would be shifting the number right instead of left, and masking with 1.
The block of code creating out[j] works just fine.
Your problem is in the output block, due to use of 0x8000. Whenever k >= 16, the low 16 bits will be zero, guaranteeing that 0x8000 is zero.
Your code seems overly complicated to me. Here's my version of a C program that transforms a string of 1's and 0's into an int and one going from int to string.
#include <stdlib.h>
#include <stdio.h>
int main(int argc, char **argv);
int main (int argc, char **argv) {
char str [] = "1010101010101010";
int x;
int out;
for (x=0;x<16;x++) {
if (str[x] == '1') {
out |= (1 << x);
}
}
printf("%d", out) ;
}
and
#include <stdlib.h>
#include <stdio.h>
int main(int argc, char **argv);
int main (int argc, char **argv) {
char str [] = "1010101010101010";
int in = 21845;
char out[17] = {0};
for (x=0;x<16;x++) {
if (in & (1<<x)) {
out[x] = '1';
}
else {
out[x] = '0';
}
}
printf("%s", out) ;
}
good afternoon.
I got the code below on a book. I'm trying to execute it, but I don't know what is the "first" and "last" parameters on the MakeCodeWritable function, or where I can find them. Someone can help? This code is about C obfuscation method. I'm using Xcode program and LLVM GCC 4.2 compiler.
#include <stdio.h>
#include <sys/mman.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
typedef unsigned int uint32;
typedef char* caddr_t;
typedef uint32* waddr_t;
#define Tam_celula 64
#define ALIGN __attribute__((aligned(Tam_celula)))
void makeCodeWritable(char* first, char* last) {
char* firstpage = first - ((int)first % getpagesize());
char* lastpage = last - ((int)last % getpagesize());
int pages = (lastpage-firstpage)/getpagesize()+1;
if (mprotect(firstpage,pages*getpagesize(), PROT_READ|PROT_EXEC|PROT_WRITE)==-1) perror("mprotect");
}
void xor(caddr_t from, caddr_t to, int len){
int i;
for(i=0;i<len;i++){
*to ^= *from; from++; to++;
} }
void swap(caddr_t from, caddr_t to, int len){
int i;
for(i=0;i<len;i++){
char t = *from; *from = *to; *to = t; from++; to++;
} }
#define CELLSIZE 64
#define ALIGN asm volatile (".align 64\n");
void P() {
static int firsttime=1; if (firsttime) {
xor(&&cell5,&&cell2,CELLSIZE);
xor(&&cell0,&&cell3,CELLSIZE);
swap(&&cell1,&&cell4,CELLSIZE);
firsttime = 0; }
char* a[] = {&&align0,&&align1,&&align2,&&align3,&&align4,&&align5};
char*next[] ={&&cell0,&&cell1,&&cell2,&&cell3, &&cell4,&&cell5};
goto *next[0];
align0: ALIGN
cell0: printf("SPGM0\n");
xor(&&cell0,&&cell3,3*CELLSIZE);
goto *next[3];
align1: ALIGN
cell1: printf("SPGM2\n"); xor(&&cell0,&&cell3,3*CELLSIZE);
goto *next[4];
align2: ALIGN
cell2: printf("SPGM4\n"); xor(&&cell0,&&cell3,3*CELLSIZE);
goto *next[5];
align3: ALIGN
cell3: printf("SPGM1\n"); xor(&&cell3,&&cell0,3*CELLSIZE);
goto *next[1];
align4: ALIGN
cell4: printf("SPGM3\n"); xor(&&cell3,&&cell0,3*CELLSIZE);
goto *next[2];
align5: ALIGN
cell5: printf("SPGM5\n");
xor(&&cell3,&&cell0,3*CELLSIZE);
}
int main (int argc, char *argv[]) {
makeCodeWritable(...);
P(); P();
}
The first argument should be (char *)P, because it looks like you want to modify code inside function P. The second argument is the ending address of function P. You can first compile the code, and using objdump -d to see the address of beginning and end of P, then calculate the size of the function, SIZE, then manually specify in the makeCodeWritable( (char *)P, ((char *)P) + SIZE.
The second way is utilizing the as to get the size of function P, but it depends on the assembler language on your platform. This is code snipe I modified from your code, it should be able to compile and run in x86, x86_64 in GCC 4.x on Linux platform.
align5: ALIGN
cell5: printf("SPGM5\n");
xor(&&cell3,&&cell0,3*CELLSIZE);
// adding an label to the end of function P to assembly code
asm ("END_P: \n");
;
}
extern char __sizeof__myfunc[];
int main (int argc, char *argv[]) {
// calculate the code size, ending - starting address of P
asm (" __sizeof__myfunc = END_P-P \n");
// you can see the code size of P
printf("code size is %d\n", (unsigned)__sizeof__myfunc);
makeCodeWritable( (char*)P, ((char *)P) + (unsigned)__sizeof__myfunc);
P(); P();
}
With some modification to support LLVM GCC and as in Mac OS X
int main (int argc, char *argv[]) {
size_t sizeof__myfunc = 0;
asm volatile ("movq $(_END_P - _P),%0;"
: "=r" (sizeof__myfunc)
: );
printf("%d\n", sizeof__myfunc);
I'm gating more then 1000 page faults in this program.
can i reduce them to some smaller value or even to zero ?
or even any other changes can speed up the execution
#include <stdio.h>
#include<stdlib.h>
int main(int argc, char* argv[])
{
register unsigned int u, v,i;
register unsigned int arr_size=0;
register unsigned int b_size=0;
register unsigned int c;
register unsigned int *b;
FILE *file;
register unsigned int *arr;
file=fopen(argv[1],"r");
arr=(unsigned int *)malloc(4*10000000);
while(!feof(file)){
++arr_size;
fscanf(file,"%u\n",&arr[arr_size-1]);
}
fclose(file);
b=(unsigned int *)malloc(arr_size*4);
if (arr_size!=0)
{
++b_size;
b[b_size-1]=0;
for (i = 1; i < arr_size; ++i)
{
if (arr[b[b_size-1]] < arr[i])
{
++b_size;
b[b_size-1]=i;
continue;
}
for (u = 0, v = b_size-1; u < v;)
{
c = (u + v) / 2;
if (arr[b[c]] < arr[i]) u=c+1; else v=c;
}
if (arr[i] < arr[b[u]])
{
b[u] = i;
}
if(i>arr_size)break;
}
}
free(arr);
free(b);
printf("%u\n", b_size);
return 0;
}
The line:
arr=(unsigned int *)malloc(4*10000000);
is not a good programming style. Are you sure that your file is as big as 40MBs? try not to allocate the whole memory in the first lines of your program.