I have this:
Serial.write(charBuf[0]); //gives 5
String data(charBuf);
Serial.write(data); //gives nothing (space)
first is prints 5 , second prints nothing. What am i missing? is it has to do with NULL terminated stuff?
This is how the buffer is being created:
int len=1;
char charBuf[len];
for(int k=ACT_THRESH;k<ACT_THRESH+len;k++)
{
charBuf[k-ACT_THRESH]= EEPROM.read(k);
}
int len = 1;
int str_len = 0;
char charBuf[16];
for(int k = ACT_THRESH; k < ACT_THRESH + len && str_len < sizeof(charBuf); k++)
{
charBuf[str_len++]= EEPROM.read(k);
}
charBuf[str_len] = '\0';
But I don't get the goal of the loop if len = 1
Related
Why do I get a segfault when I try to print the strlen of a string, which is part of an array of strings? I can print each string - the printf works perfectly. But why does the strlen cause a segfault?
The below program first takes an input n, which is the number of strings I want to dynamically allocate. Then I allocate space for 32 bytes for each string
int main() {
int i;
int n;
char **nums;
scanf("%d", &n);
printf("n = %d\n", n);
nums = malloc(sizeof(char *) * n);
printf("allocated nums\n");
for(i=0; i<n; i++) {
nums[i] = malloc(sizeof(char) * 32);
memset(nums[i], '\0', sizeof(char) * 32);
}
for(i=0; i < n; i++) {
scanf("%s", &nums[i]);
}
for(i=0; i<n; i++) {
// THIS PRINTS FINE
printf("string = %s\n", &nums[i]);
// SEGFAULT HERE IMMEDIATELY
printf("length = %d\n", strlen(nums[i]));
}
Here is the console output. As a test, I entered in n=3, followed by the numbers 45, 46, and 47:
3
n = 3
allocated nums
45
46
47
string = 45
Segmentation fault (core dumped)
Additionally, I get a segfault when I try to access an individual character in each string. Again, the first printf in outer for loop prints the string, then I get a segfault accessing nums[i][k]:
int i, k=0;
for(i=0; i<n; i++) {
printf("Printiiing: %s\n", &nums[i]);
// WHY DOES THIS SEGFAULT???
//printf("first char = %c\n", nums[i][0]);
while(k<32 && nums[i][k] != '\0') {
// THIS CAUSES A SEG FAULT
printf("char = %c", (nums[i])[k]);
k++;
}
}
This is fine:
for(i=0; i<n; i++) {
nums[i] = malloc(sizeof(char) * 32);
memset(nums[i], '\0', sizeof(char) * 32);
}
After this loop, each nums[i] is a pointer to 32-byte buffer.
But this corrupts (overwrites) all the pointers, instead of reading strings into the allocated buffers:
for(i=0; i < n; i++) {
scanf("%s", &nums[i]);
}
To fix the bug, use: scanf("%s", nums[i]);.
There is the difference pointer between the &nums[i] and nums[i] address. You can check with the strlen((const char*)(&nums[i])) for get length.
The explanation of #Employee of Russia is exactly for reason.
I need to implement a Rc4 algorithm with a seed: 1 2 3 6 and the plain text cryptology. I am following this guideline we were provided in class, but it's not initializing S correctly.
my output is
and needs to be
My code was previously printing negative values , not sure why but I managed to fix that error. Thought everything was good to go but it's not. Sorry for the pictures, I figured it was easier to explain what I was following for my code structure. I am mod 4 the seed since it contains 4 characters, could that possibly be my error?
#include <iostream>
#include <string>
#include <string.h>
using std::endl;
using std::string;
void swap(unsigned int *x, unsigned int *y);
int main()
{
string plaintext = "cryptology";
char cipherText[256] = { ' ' };
unsigned int S[256] = { 0 };
unsigned int t[256] = { 0 };
unsigned int seed[4] = { 1, 2, 3, 6 }; // seed used for test case 1
unsigned int temp = 0;
int runningTotal = 0;
unsigned int key = 0;
// inilializing s and t
for (int i = 0; i < 256; i++)
{
S[i] = i;
t[i] = seed[i % 4];
}
for (int i = 0; i < 256; i++)
{
runningTotal += S[i] + t[i];
runningTotal %= 256;
swap(&S[runningTotal], &S[i]);
std::cout << S[i] <<" ";
}
runningTotal = 0;
for (int i = 0; i < plaintext.size(); i++)
{
runningTotal %= 256;
swap(&S[i], &S[runningTotal]);
temp = (unsigned int)S[i] + (unsigned int)S[runningTotal];
temp %= 256;
key = S[temp];
std::cout << endl;
cipherText[i] = plaintext[i] ^ key;
}
std::cout << " this is cipher text " << endl;
std::cout << cipherText << endl;
system("pause");
return 0;
}
void swap(unsigned int *x, unsigned int *y)
{
unsigned int temp = 0;
temp = *x;
*x = *y;
*y = temp;
}
Actually I think you're generating S[] correctly. I can only assume you're supposed to do something different with the key. (Perhaps's its an ASCII string instead of four byte values? Check your assignment notes.)
There is a problem later on, however. In the stream generation loop, you're supposed to do the increment and swap operations before you fetch a byte from S[].
for (int k = 0; k < plaintext.size(); k++)
{
i = (i+1) % 256; // increment S[] index
runningTotal = (runningTotal + S[i]) % 256; // swap bytes
swap(&S[i], &S[runningTotal]);
temp = (S[i] + S[runningTotal]) % 256; // fetch byte from S and
cipherText[k] = plaintext[k] ^ S[temp]; // XOR with plaintext
}
NOTE: Although unrelated to your question, your code could be made a lot tidier by using unsigned char values instead of ints. That would eliminate the % 256 instructions that are littered all over the place. (But be careful during initialization, because i<256 will always be true if i is an unsigned char.)
This dynamic programming algorithm is returning unhandled exception error probably due to the two dimensional arrays that I am using for various (and very large) number of inputs. I can't seem to figure out the issue here. The complete program as follows:
// A Dynamic Programming based solution for 0-1 Knapsack problem
#include<stdio.h>
#include<stdlib.h>
#define MAX 10000
int size;
int Weight;
int p[MAX];
int w[MAX];
// A utility function that returns maximum of two integers
int maximum(int a, int b) { return (a > b) ? a : b; }
// Returns the maximum value that can be put in a knapsack of capacity W
int knapSack(int W, int wt[], int val[], int n)
{
int i, w;
int retVal;
int **K;
K = (int**)calloc(n+1, sizeof(int*));
for (i = 0; i < n + 1; ++i)
{
K[i] = (int*)calloc(W + 1, sizeof(int));
}
// Build table K[][] in bottom up manner
for (i = 0; i <= n; i++)
{
for (w = 0; w <= W; w++)
{
if (i == 0 || w == 0)
K[i][w] = 0;
else if (wt[i - 1] <= w)
K[i][w] = maximum(val[i - 1] + K[i - 1][w - wt[i - 1]], K[i - 1][w]);
else
K[i][w] = K[i - 1][w];
}
}
retVal = K[n][W];
for (i = 0; i < size + 1; i++)
free(K[i]);
free(K);
return retVal;
}
int random_in_range(unsigned int min, unsigned int max)
{
int base_random = rand();
if (RAND_MAX == base_random) return random_in_range(min, max);
int range = max - min,
remainder = RAND_MAX % range,
bucket = RAND_MAX / range;
if (base_random < RAND_MAX - remainder) {
return min + base_random / bucket;
}
else {
return random_in_range(min, max);
}
}
int main()
{
srand(time(NULL));
int val = 0;
int i, j;
//each input set is contained in an array
int batch[] = { 10, 20, 30, 40, 50, 5000, 10000 };
int sizeOfBatch = sizeof(batch) / sizeof(batch[0]);
//algorithms are called per size of the input array
for (i = 0; i < sizeOfBatch; i++){
printf("\n");
//dynamic array allocation (variable length to avoid stack overflow
//calloc is used to avoid garbage values
int *p = (int*)calloc(batch[i], sizeof(int));
int *w = (int*)calloc(batch[i], sizeof(int));
for (j = 0; j < batch[i]; j++){
p[j] = random_in_range(1, 500);
w[j] = random_in_range(1, 100);
}
size = batch[i];
Weight = batch[i] * 25;
printf("| %d ", batch[i]);
printf(" %d", knapSack(Weight, w, p, size));
free(p);
free(w);
}
_getch();
return 0;
}
Change this:
for (i = 0; i < size + 1; i++)
free(K[i]);
free(K);
return K[size][Weight];
To this:
int retVal;
...
retVal = K[size][Weight];
for (i = 0; i < size + 1; i++)
free(K[i]);
free(K);
return retVal;
So, my assignment is to write a spell check program and then parallelize it using openMPI. My take was to load the words from a text file into my array called dict[] and this is used as my dictionary. Next, I get input from the user and then it's supposed go through the dictionary array and check whether the current word is within the threshold percentage, if it is, print it out. But I'm only supposed to print out a certain amount of words. My problem is, is that, my suggestions[] array, doesn't seem to fill up the way I need it to, and it gets a lot of blank spots in it, whereas, I thought at least, is that the way I wrote it, is to just fill it when a word is within threshold. So it shouldn't get any blanks in it until there are no more words being added. I think it's close to being finished but I can't seem to figure this part out. Any help is appreciated.
#include <stdio.h>
#include <mpi.h>
#include <string.h>
#include <stdlib.h>
#define SIZE 30
#define max(x,y) (((x) > (y)) ? (x) : (y))
char *dict[50000];
char *suggestions[50000];
char enterWord[50];
char *myWord;
int wordsToPrint = 20;
int threshold = 40;
int i;
int words_added = 0;
int levenshtein(const char *word1, int len1, const char *word2, int len2){
int matrix[len1 + 1][len2 + 1];
int a;
for(a=0; a<= len1; a++){
matrix[a][0] = a;
}
for(a=0;a<=len2;a++){
matrix[0][a] = a;
}
for(a = 1; a <= len1; a++){
int j;
char c1;
c1 = word1[a-1];
for(j = 1; j <= len2; j++){
char c2;
c2 = word2[j-1];
if(c1 == c2){
matrix[a][j] = matrix[a-1][j-1];
}
else{
int delete, insert, substitute, minimum;
delete = matrix[a-1][j] +1;
insert = matrix[a][j-1] +1;
substitute = matrix[a-1][j-1] +1;
minimum = delete;
if(insert < minimum){
minimum = insert;
}
if(substitute < minimum){
minimum = substitute;
}
matrix[a][j] = minimum;
}//else
}//for
}//for
return matrix[len1][len2];
}//levenshtein
void prompt(){
printf("Enter word to search for: \n");
scanf("%s", &enterWord);
}
int p0_compute_output(int num_processes, char *word1){
int totalNumber = 0;
int k = 0;
int chunk = 50000 / num_processes;
for(i = 0; i < chunk; i++){
int minedits = levenshtein(word1, strlen(word1), dict[i], strlen(dict[i]));
int thresholdPercentage = (100 * minedits) / max(strlen(word1), strlen(dict[i]));
if(thresholdPercentage < threshold){
suggestions[totalNumber] = dict[i];
totalNumber = totalNumber + 1;
}
}//for
return totalNumber;
}//p0_compute_output
void p0_receive_output(int next_addition){
int num_to_add;
MPI_Comm comm;
MPI_Status status;
MPI_Recv(&num_to_add,1,MPI_INT,MPI_ANY_SOURCE, MPI_ANY_TAG,MPI_COMM_WORLD, MPI_STATUS_IGNORE);
printf("--%d\n", num_to_add);
suggestions[next_addition] = dict[num_to_add];
next_addition = next_addition + 1;
}
void compute_output(int num_processes, int me, char *word1){
int chunk = 0;
int last_chunk = 0;
MPI_Comm comm;
if(50000 % num_processes == 0){
chunk = 50000 / num_processes;
last_chunk = chunk;
int start = me * chunk;
int end = me * chunk + chunk;
for(i = start; i < end;i++){
int minedits = levenshtein(word1, strlen(word1), dict[i], strlen(dict[i]));
int thresholdPercentage = (100 * minedits) / max(strlen(word1), strlen(dict[i]));
if(thresholdPercentage < threshold){
int number_to_send = i;
MPI_Send(&number_to_send, 1, MPI_INT, 0, 1, MPI_COMM_WORLD);
}
}
}
else{
chunk = 50000 / num_processes;
last_chunk = 50000 - ((num_processes - 1) * chunk);
if(me != num_processes){
int start = me * chunk;
int end = me * chunk + chunk;
for(i = start; i < end; i++){
int minedits = levenshtein(word1, strlen(word1), dict[i], strlen(dict[i]));
int thresholdPercentage = (100 * minedits) / max(strlen(word1), strlen(dict[i]));
if(thresholdPercentage < threshold){
int number_to_send = i;
MPI_Send(&number_to_send, 1, MPI_INT, 0, 1, MPI_COMM_WORLD);
}//if
}//for
}//if me != num_processes
else{
int start = me * chunk;
int end = 50000 - start;
for(i = start; i < end; i++){
int minedits = levenshtein(word1, strlen(word1), dict[i], strlen(dict[i]));
int thresholdPercentage = (100 * minedits) / max(strlen(word1), strlen(dict[i]));
if(thresholdPercentage < threshold){
int number_to_send = i;
MPI_Send(&number_to_send, 1, MPI_INT, 0, 1, MPI_COMM_WORLD);
}
}
}//me == num_processes
}//BIG else
return;
}//COMPUTE OUTPUT
void set_data(){
prompt();
MPI_Bcast(&enterWord,20 ,MPI_CHAR, 0, MPI_COMM_WORLD);
}//p0_send_inpui
//--------------------------MAIN-----------------------------//
main(int argc, char **argv){
int ierr, num_procs, my_id, loop;
FILE *myFile;
loop = 0;
for(i=0;i<50000;i++){
suggestions[i] = calloc(SIZE, sizeof(char));
}
ierr = MPI_Init(NULL, NULL);
ierr = MPI_Comm_rank(MPI_COMM_WORLD, &my_id);
ierr = MPI_Comm_size(MPI_COMM_WORLD, &num_procs);
printf("Check in from %d of %d processors\n", my_id, num_procs);
set_data();
myWord = enterWord;
myFile = fopen("words", "r");
if(myFile != NULL){
for(i=0;i<50000;i++){
dict[i] = calloc(SIZE, sizeof(char));
fscanf(myFile, "%s", dict[i]);
}//for
fclose(myFile);
}//read word list into dictionary
else printf("File not found");
if(my_id == 0){
words_added = p0_compute_output(num_procs, enterWord);
printf("words added so far: %d\n", words_added);
p0_receive_output(words_added);
printf("Threshold: %d\nWords To print: %d\n%s\n", threshold, wordsToPrint, myWord);
ierr = MPI_Finalize();
}
else{
printf("my word %s*\n", enterWord);
compute_output(num_procs, my_id, enterWord);
// printf("Process %d terminating...\n", my_id);
ierr = MPI_Finalize();
}
for(i=0;i<wordsToPrint;i++){
printf("*%s\n", suggestions[i]);
}//print suggestions
return (0);
}//END MAIN
Here are a few problems I see with what you're doing:
prompt() should only be called by rank 0.
The dictionary file should be read only by rank 0, then broadcast the array out to the other ranks
Alternatively, have rank 1 read the file while rank 0 is waiting for input, broadcast input and dictionary afterwards.
You're making the compute_output step overly complex. You can merge p0_compute_output and compute_output into one routine.
Store an array of indices into dict in each rank
This array will not be the same size in every rank, so the simplest way to do this would be to send from each rank a single integer indicating the size of the array, then send the array with this size. (The receiving rank must know how much data to expect). You could also use the sizes for MPI_Gatherv, but I expect this is more than you're wanting to do right now.
Once you have a single array of indices in rank 0, then use this to fill suggestions.
Save the MPI_Finalize call until immediately before the return call
For the final printf call, only rank 0 should be printing that. I suspect this is causing a large part of the "incorrect" result. As you have it, all ranks are printing suggestions, but it is only filled in rank 0. So the others will all be printing blank entries.
Try some of these changes, especially the last one, and see if that helps.
I'm trying to take to the following input:
1
4
47 2 4 43577
The part of my code that deals with this is:
for (scanf("%d", &t); t --; )
{
int count = 0;
scanf("%d",&n);
for (int i = 0, x; i < n; ++ i)
{
scanf("%d",&x);
str = to_string(x);
f4[i] = get_count(str,'4');
f7[i] = get_count(str,'7');
}
However, with this I get a runtime error, which shows an access violation in the file free.c.
But, when I try to debug it, it runs well in the debug mode and gives the correct answer.
Also, when I output the variable x right after I input it, the program works well in runtime as well. This is shown in the following code, which runs fine in runtime as well:
for (scanf("%d", &t); t --; )
{
int count = 0;
scanf("%d",&n);
for (int i = 0, x; i < n; ++ i)
{
scanf("%d",&x);
cout<<"A"<<i<<" is "<<x<<'\n';
str = to_string(x);
f4[i] = get_count(str,'4');
f7[i] = get_count(str,'7');
}
Any idea why this may be happening?
Some of the stackoverflow users are saying that the code runs fine. I'm using VS 2012. Can this be something that is compiler specific?
The complete code:
#include<iostream>
#include<conio.h>
#include<string>
#include<math.h>
using namespace std;
int get_count(string s, char x)
{
int count = 0;
int l = s.length();
for(int i = 0; i < l;i++)
{
if (s[i] == x)
count++;
}
return count;
}
void main()
{
int * f4 = new int;
int * f7 = new int;
string * back = new string;
int n = 0;
int t = 0;
string str;
for (scanf("%d", &t); t --; )
{
int count = 0;
scanf("%d",&n);
for (int i = 0, x; i < n; ++ i)
{
scanf("%d",&x);
str = to_string(x);
f4[i] = get_count(str,'4');
f7[i] = get_count(str,'7');
}
for(int i = 0;i < n;i++)
{
for(int j = i; j < n;j++)
{
int c4 = 0;
int c7 = 0;
for(int k = i; k <= j;k++)
{
c4 += f4[k];
c7 += f7[k];
}
double value = pow((double)c4,(double)c7);
if(value <= (double)(j - i + 1)&&(c4!=2)&&(c7!=2))
{
count++;
//cout<<"yes"<<'\t';
}
}
}
cout<<"Ans: "<<count<<'\n';
}
//getch();
}
There are no other variable assignments apart from those in this code.
The exact error that I get with runtime is:
Unhandled exception at 0x7794E3BE (ntdll.dll) in Practice1.exe: 0xC0000005: Access violation reading location 0x38389246.
You did not include the "get_count" function. I think it has something to do with that function. I rewrote that function to return some number and I don't get that error. Try to assert that you are not attempting to use a null pointer in that function.
Works fine on my machine:
Here's what I changed
for (int i = 0, x; i < n; ++ i)
{
scanf("%d",&x);
stringstream ss;
ss << x;
str = ss.str();
f4[i] = get_count(str,'4');
f7[i] = get_count(str,'7');
}
Output:
1
4
47 2 4 43577
Ans: 5