I have this program:
#include <iostream>
#include <vector>
#include <map>
#include <string>
#include <sstream>
#include <algorithm>
int main(int argc, const char * argv[]) {
std::vector<int> task_scores;
int n;
std::cin >> n;
for(int i = 0; i < n; i++) {
int sc;
std::cin >> sc;
task_scores.push_back(sc);
}
std::map<std::string, std::vector<size_t>> student_solutions;
std::string command = "";
while(true) {
std::vector<std::string> tok_com;
getline(std::cin, command);
std::stringstream strstream(command);
std::string token = "";
while (getline(strstream, token, ' ')) {
std::cout << token;
tok_com.push_back(token);
}
if (tok_com[0] == "SOLVED") {
std::string name = tok_com[1];
int task = std::stoi(tok_com[2]);
if(std::find(student_solutions[name].begin(), student_solutions[name].end(), task) !=
student_solutions[name].end()) {
student_solutions[name].push_back(task);
}
}
}
return 0;
}
If you comment out if clause, then code works just fine. But if you don't, the code stops with EXC_BAD_ACCESS when trying to cout the token. How can this happen?
But if you don't, the code stops with EXC_BAD_ACCESS when trying to cout the token. How can this happen?
if (tok_com[0] == "SOLVED") {
// ^^^
requires that at least one value was actually stored into the tok_com vector within your loop before.
You should test for tok_com.empty() before dereferencing tok_com:
if (!tok_com.empty() && tok_com[0] == "SOLVED") {
// ^^^^^^^^^^^^^^^^^^^
// ...
}
What you're experiencing actually is undefined behavior varying from exploding fridges, little demons flying out from your nostrils or simply exceptions thrown by your debugging environment or operating system.
Related
I am having what seems to be a common issue however reading through the replies to the similar questions I can't find the solution to my issue at all as I have already done what they are suggesting such as making the variable an array. I have the following code:
#include "stdafx.h"
#include <cstring>
#include <fstream>
#include <iostream>
#include <string>
#include <algorithm>
#include <future>
using namespace std;
string eng2Str[4] = { "money", "politics", "RT", "#"};
int resArr[4];
int main()
{
engine2(eng2Str[4], resArr[4]);
system("Pause");
system("cls");
return 0;
}
void engine2(string &eng2Str, int &resArr)
{
ifstream fin;
fin.open("sampleTweets.csv");
int fcount = 0;
string line;
for (int i = 0; i < 4; i++) {
while (getline(fin, line)) {
if (line.find(eng2Str[i]) != string::npos) {
++fcount;
}
}
resArr[i] = fcount;
}
fin.close();
return;
}
Before you mark as duplicate I have made sure of the following:
The array and variable I am trying to assign are both int
Its an array
The error is:
expression must have pointer-to-object type
The error is occurring at the "resArr[i] = fcount;" line and am not sure why as resArr is an int array and I am trying to assign it a value from another int variable. I am quite new to C++ so any help would be great as I am really stuck!
Thanks!
The problem is that you've declared your function to take a reference to a single string and int, not arrays. It should be:
void engine2(string *eng2Str, int *resArr)
or:
void engine2(string eng2Str[], int resArr[])
Then when you call it, you can give the array names as arguments:
engine2(eng2Str, resArr);
Another problem is the while loop in the function. This will read the entire file during the first iteration of the for() loop. Other iterations will not have anything to read, since it will be at the end of the file already. You could seek back to the beginning of the file, but a better way would be to rearrange the two loops so you just need to read the file once.
while (getline(fin, line)) {
for (int i = 0; i < 4; i++) {
if (line.find(eng2Str[i]) != string::npos) {
resArr[i]++;
}
}
}
I would suggest to use std::vector instead of pure C array.
In your code, there are more issues.
You are passing the fourth element of both arrays to the engine2 function.
From your definition of void engine2(string &eng2Str, int &resArr) you expect reference to a string (not array / vector) and an address / reference of int - you need to pass an pointer to the first element of resArr.
#include <cstring>
#include <fstream>
#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <future>
using namespace std;
vector<string> eng2Str = { "money", "politics", "RT", "#" };
int resArr[4] = {};
void engine2(const vector<string>& eng2Str, int* resArr)
{
ifstream fin;
fin.open("sampleTweets.csv");
int fcount = 0;
string line;
for (int i = 0; i < 4; i++)
{
while (getline(fin, line))
{
if (line.find(eng2Str[i]) != string::npos)
{
++fcount;
}
}
resArr[i] = fcount;
}
fin.close();
return;
}
int main()
{
engine2(eng2Str, resArr);
system("Pause");
system("cls");
return 0;
}
I have an input file that looks like this
1 0 3
2 11 5
3 15 1
4 16 11
and a structure that looks like this
struct numb {
int numb1;
int numb2;
int numb3;
}
and I need to create an array of the struct so that each element of the array holds all three numbers. So
numbArray[0].numb1 == 1
numbArray[0].numb2 == 0
numbArray[0].numb3 == 3
numbArray[1].numb1 == 2
numbArray[1].numb2 == 11
and so on. I've gotten the hang of opening and closing files, finding how many lines there are in a file, and reading a single line from a file, but I do not know how to store individual elements from a line.
My program looks like this so far:
#include <iostream>
#include <fstream>
#include <string>
int main(int argc, char* argv[])
{
ifstream inFile(argv[1]);
int fileLength = 0;
std::string line;
while(std::getline(inFile, line))
{
++fileLength;
}
struct numb {
int numb1;
int numb2;
int numb3;
}
if(inFile.is_open())
{
for(unsigned i = 0; i <= fileLength; i++)
{
//What to do here?
}
}
}
Use getline when you don't have regular structure to the input and need to handle variation between lines. When your input file has regular structure (in this case, there are always three values per line), then simply use the stream extraction operators directly:
#include <iostream>
#include <vector>
struct group
{
int n1;
int n2;
int n3;
};
int main()
{
std::vector<group> groups;
while (std::cin)
{
group line;
line.n1 << std::cin;
line.n2 << std::cin;
line.n3 << std::cin;
groups.push_back(group);
}
}
Express your ideas directly in code as much as possible.
Note I've written the code assuming that the file is in the proper form. If there are too many or too few values per line, then the above code will be confused. However, it is best to code the simplest thing that could possibly work and worry about complexity when you need it. In your example you stated that the input file was well-formed, so there's no need to overcomplicate things.
I recommend using a std::stringstream for this:
#include <iostream>
#include <sstream>
#include <string>
#include <stdio.h>
#include <vector>
struct numb {
int numb1;
int numb2;
int numb3;
};
void populate(std::vector<numb>& my_numbs, std::string line) {
std::stringstream ss(line);
numb my_numb;
ss >> my_numb.numb1 >> my_numb.numb2 >> my_numb.numb3;
my_numbs.push_back(my_numb);
}
void output(const numb my_numbs) {
printf("%d %d %d\n", my_numbs.numb1, my_numbs.numb2, my_numbs.numb3);
}
int main(int argc, char* argv[]) {
ifstream inFile(argv[1]);
std::string line;
std::vector<numb> my_vect;
while(std::getline(inFile, line)) {
populate(my_vect, line);
}
for(size_t i = 0; i < my_vect.size(); ++i) {
std::cout << "my_vect[" << i << "]:";
output(my_vect[i]);
}
return 0;
}
std::stringstreams allow you to parse out data types from std::strings, you you just need to parse out 3 ints, which you can use with your struct. You then push the struct into your vector.
Here's the working ideone taking input from stdin.
You should probably be able to do something like this:
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
using namespace std;
int main(int argc, char* argv[])
{
ifstream inFile(argv[1]);
int fileLength = 0;
std::string line;
struct numb {
int numb1;
int numb2;
int numb3;
};
vector<vector<int>> sets;
int n1, n2, n3;
while (std::cin >> n1)
{
cin >> n2;
cin >> n3;
vector<int> vec;
vec.push_back(n1);
vec.push_back(n2);
vec.push_back(n3);
sets.push_back(vec);
}
numb * numbSet = new numb[sets.size()];
//Since the vectors data is continuous in memory just as the array of structs are
//you can just copy the data directly
for (int i = 0; i < sets.size(); i++)
{
std::memcpy(&numbSet[i], &sets[i][0], sizeof(numb));
}
}
I am trying to code a program where it takes a program as an input and prints out all the comments written in that program in a separate line.
#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
int main() {
string str;
while(getline(cin,str)) {
int i;
// cout<<str;
for(i=0;str[i]!='/' && str[i+1] !='/';i++);
//cout<<i;
for(i;str[i]!='\n';i++) {
// cout<<i;
cout<<str[i];
}
cout<<endl;
}
return 0;
}
I am getting a segmentation fault in this code and I can't understand why. This is part of a code of a problem in hackerrank https://www.hackerrank.com/challenges/ide-identifying-comments/copy-from/12957153
As commented in your question your code is wrong. First you are treating std::string object, returned by getline, as character array. Secondly your for loops never end if there is no // or \n found in input string. So obviously it will crash. Below is the modified code.
#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
int main() {
string str;
while(getline(cin,str)) {
int i;
// cout<<str;
size_t len = str.length();
const char *cstr = str.c_str();
for(i=0; (cstr[i]!='/' && cstr[i+1] !='/' && i < len); i++)
//cout<<i;
for(; cstr[i]!='\n' && i < len;i++) {
// cout<<i;
cout<<cstr[i];
}
cout<<endl;
}
return 0;
}
int main() {
while(getline(cin,str)) {
int i, len = str.size();
//always make sure that you are not accessing
//contents after your string has ended
for(i=0; i < (len - 1) && !(str[i] == '/' && str[i+1] == '/'); i++);
//note that i here might be the last alphabet
//if there's no comment
if(i < len && str[i] != '/')
i++;
//checking if str[i] != '\n' is not a good idea
//as c++ stl strings are not temrinated by '\n'
if(i < len) {
for(; i < len; i++)
cout << str[i];
cout << endl;
}
}
return 0;
}
Also note that both of the following codes won't terminate at the 4th character, c++ stl strings are not terminated by these characters.
string str = "hahahaha";
str[4] = '\n';
cout << str;
str[4] = '\0';
cout << str;
This is much easier to write and probably much faster than the other solutions to date.
#include <iostream>
int main()
{
std::string str;
while (std::getline(std::cin, str))
{
size_t loc = str.find("//");
if (loc != str.npos)
{
std::cout << str.substr(loc + 2)<< std::endl;
}
}
return 0;
}
It is also wrong.
Here is a nice, clean, and simple state machine version. Also pretty close to worst-case for speed. Thing is it's closest to being right, even though it is also wrong.
#include <iostream>
enum states
{
seeking1,
seeking2,
comment
};
int main()
{
std::string str;
while (std::getline(std::cin, str))
{
states state = seeking1;
for (char ch:str)
{
switch (state)
{
case seeking1:
if (ch == '/')
{
state = seeking2;
}
break;
case seeking2:
if (ch == '/')
{
state = comment;
}
else
{
state = seeking1;
}
break;
case comment:
std::cout << ch;
break;
}
}
if (state == comment)
{
std::cout << std::endl;
}
}
return 0;
}
Why are these approaches all wrong? Consider the line
cout << "Hi there! I am \\Not A Comment!" << endl;`
You can't just look at the \\, you also need the context. This is why the state machine above is the better option. It can be modified to handle, at the very least, states for handling strings and block comments.
Consider a simple program. It must take string from stdin and save to variable.
It is not stated how many lines of input will be taken, but program must terminate if meet newline.
For example:
stdin:
abc
abs
aksn
sjja
\n
I tried but it doesn't work. Here is my code:
#include <iostream>
#include <cstring>
#include <cstdio>
using namespace std;
// Constant
#define max 100000
struct chuoi
{
char word[10];
};
chuoi a[max];
void readStr()
{
int i=0;
while ( fgets(a[i].word, 10,stdin) != NULL)
{
if (a[i].word[0] == ' ') break;
a[i].word[strlen(a[i].word)-1] = '\0'; //replaced \n by \0
i++;
}
//length = i;
}
int main()
{
readStr();
return 0;
}
So, how to solve this problem?
One alternative here is to use std::getline to get each line. If the line is empty, or the input fails, then exit the loop.
void readStr()
{
std::string str;
while ( std::getline(std::cin, str) && str.length() )
{
// use the string...
}
}
Adding the std::getline and use of std::vector to your sample code, and keeping with the spirit of your original sample;
#include <string>
#include <iostream>
#include <vector>
const std::size_t Max = 100000;
struct chuoi
{
explicit chuoi(std::string const& str) : word(str)
{
}
std::string word;
};
void readStr(std::vector<chuoi>& a)
{
std::string str;
while ( std::getline(std::cin, str) && str.length() )
{
a.push_back(chuoi(str));
}
}
void writeStr(std::vector<chuoi> const& a)
{
for (auto i = a.begin(); i != a.end(); ++i) {
std::cout << i->word << std::endl;
}
}
int main()
{
std::vector<chuoi> a;
a.reserve(Max);
readStr(a);
writeStr(a);
return 0;
}
To solve you immediate problem, minimal changes in the code can be made as follows;
void readStr()
{
int i = 0;
while ( fgets(a[i].word, 10, stdin) != NULL)
{
a[i].word[strlen(a[i].word) - 1] = '\0'; // transform the end of line character to NULL
if (strlen(a[i].word) == 0) {
break;
}
i++;
}
}
If the standard input will always be used (stdin), the gets function can also be used;
while ( gets(a[i].word) != NULL)
{
if (strlen(a[i].word) == 0) {
break;
}
i++;
}
Notes;
fgets reads until the "enter" key on the stdin but includes the new line character
gets also reads until the return, but excludes the new line character
Both functions NULL terminate the input
Be careful of the form of gets it does not check for buffer overflow conditions
I would do something like this:
#include <string>
#include <iostream>
int main()
{
std::string line; // will contain each line of input
// Stop when line is empty or when terminal input has an error
while(std::getline(std::cin, line) && !line.empty())
{
// do stuff with line
}
}
#include <iostream>
#include <string>
#include <vector>
/*
Using STL's string class because the problem does not refer any
limits regarding the number of characters per line.
*/
using namespace std;
int main()
{
string line;
vector<string> lines;
while (getline(cin, line))
{
lines.push_back(line);
}
unsigned int i, u;
unsigned int opening = 1; // 2 if last was opening, 1 if it was closing
for (i = 0; i < (int) lines.size(); i++)
{
for (u = 0; u < (int) lines[u].length(); u++)
{
}
}
return 0;
}
I have that simple code that just reads over a few lines (input file):
"To be or not to be," quoth the Bard, "that
is the question".
The programming contestant replied: "I must disagree.
To `C' or not to `C', that is The Question!"
However, I found that it is SEGFAULTing as it reads a ' ' (space) character on the first line (4th character):
(gdb) run < texquotes_input.txt
Starting program: /home/david/src/oni/texquotes < texquotes_input.txt
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7b92533 in std::string::length() const () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
I really can't understand why, I'm not doing anything inside the loop, I'm just looping.
I already found the problem. It's the inner loop:
for (u = 0; u < (int) lines[u].length(); u++)
{
}
Should be:
for (u = 0; u < (int) lines[i].length(); u++)
{
}
In another answer the index typo was already spotted.
I'd like to add that using range-based for loops those kinds of problems are more difficult to happen, since the loop is kind of more "implicit":
#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main()
{
string line;
vector<string> lines;
while (getline(cin, line))
{
lines.push_back(line);
}
for ( const auto& currLine : lines )
{
for ( auto ch : currLine )
{
cout << ch;
}
cout << '\n';
}
}