#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';
}
}
Related
I have a small program that prints out the capital form of each letter of a word, but I get the error signed/unsigned mismatch when I compile it because I'm passing a cstring as a normal string in this program. How do I pass it correctly so that I can still use text.length()? Here is the error that I get "Tester.cpp(22,23): warning C4018: '<': signed/unsigned mismatch". It's at for (int i = 0; i < text.length(); i++)
#include <iostream>
using namespace std;
string capitalizeFirstLetter(string text);
int main() {
char sentence[100];
for ( ; ; )
{
cin.getline(sentence, 100);
if (sentence != "0")
capitalizeFirstLetter(sentence);
}
return 0;
}
string capitalizeFirstLetter(string text) {
for (int i = 0; i < text.length(); i++)
{
if (i == 0)
{
text[i] = toupper(text[i]);
}
if (text[i] == ' ')
{
++i;
text[i] = toupper(text[i]);
}
}
cout << text;
return text;
}
The simplest way to handle passing sentence as a string is to enclose it in a braced set, to provide direct initialization to the parameter std::string text eg..
for ( ; ; )
{
std::cin.getline(sentence, 100);
if (*sentence)
capitalizeFirstLetter({sentence});
}
This allows the character string sentence to be used as the Direct initialization to initialize std::string text in your capitalizeFirstLetter() function:
std::string capitalizeFirstLetter (std::string text) {
for (size_t i = 0; i < text.length(); i++)
{
if (i == 0)
{
text[i] = toupper(text[i]);
}
if (text[i] == ' ')
{
++i;
text[i] = toupper(text[i]);
}
}
std::cout << text;
return text;
}
Your complete code, after reading Why is “using namespace std;” considered bad practice?, would then be:
#include <iostream>
std::string capitalizeFirstLetter (std::string text) {
for (size_t i = 0; i < text.length(); i++)
{
if (i == 0)
{
text[i] = toupper(text[i]);
}
if (text[i] == ' ')
{
++i;
text[i] = toupper(text[i]);
}
}
std::cout << text;
return text;
}
int main (void) {
char sentence[100];
for ( ; ; )
{
std::cin.getline(sentence, 100);
if (*sentence)
capitalizeFirstLetter({sentence});
}
return 0;
}
(note: dereferencing sentence provides the first character which is then confirmed as something other than the nul-terminating character (ASCII 0))
A Better CapitalizeFirstLetter()
A slightly easier way to approach capitalization is to include <cctype> and an int to hold the last character read. Then the logic simply loops over each character and if the first character is an alpha-character, then capitalize it, otherwise only capitalize the letter when the current character is an alpha-character and the last character was whitespace, e.g.
std::string capitalizeFirstLetter (std::string text)
{
int last = 0
for (auto& c : text)
{
if (isalpha(c))
{
if (!i || isspace (last))
c = toupper(c);
}
last = c;
}
std::cout << text;
return text;
}
(note: the use of a range-based for loop above)
Either way works.
The error is not generating because of you passing a cstring as a normal string to the function but it is due to the fact that you are trying to compare c style string using != operator in the statement
if (sentence != "0")
capitalizeFirstLetter(sentence);
try using strcmp() for that
Several things bugging me here.
First off, don't use using namespace std, it's "ok" in this case, but don't get used to it, it can cause quite some trouble.
See Why is “using namespace std;” considered bad practice?
Next thing is, just use std::string instead of cstrings here, it's easier to write and to read and doesn't produce any measurable performance loss or something. And it's harder to produce bugs this way.
So just use
std::string sentence;
and
getline(std::cin, sentence);
And why do you handle the output inside the function that transforms your string? Just let the main print the transformed string.
So your main could look like this:
int main() {
std::string sentence;
while(true)
{
getline(std::cin, sentence);
auto capitalized = capitalizeFirstLetter(sentence);
std::cout << capitalized;
}
return 0;
}
PS: the 'error' you get is a warning, because you compare int i with text.length() which is of type size_t aka unsigned int or unsigned long int.
Problems with your code :
if (sentence != "0") : illegal comparison. If you want to break on getting 0 as input then try using strcmp (include <cstring>) as if (strcmp(sentence, "0"). (Note that strcmp returns 0 when two strings are equal.) Or simply do if (!(sentence[0] == '0' and sentence[1] == 0)). Moreover this condition should be accompanied with else break; to prevent the for loop from running forever.
for (int i = 0; i < text.length(); i++) : generates warning because of comparison between signed and unsigned types. Change data-type of i to string::size_type to prevent the warning.
<string> (for std::string) and <cctype> (for std::toupper) were not included.
Thanks to #john for pointing this out. Your code has undefined behaviour if last character of a string is a space. Add a check if i is still less than text.length() or not before using text[i].
Another case of error is when an space is there after 0. Move getline to condition of for to fix this. Now there will be no need to input a 0 to terminate program. Moreover, I recommend using while loop for this instead of for.
You may also need to print a newline to separate sentences. Moreover, I would prefer printing the modified sentence in the main() function using the returned string from capitalizeFirstLetter.
It doesn't matter much in short (beginner-level) codes, but avoid acquiring the habit of putting using namespace std; on the top of every code you write. Refer this.
Fixed code :
#include <cctype>
#include <cstring>
#include <iostream>
#include <string>
using namespace std;
string capitalizeFirstLetter(string text);
int main() {
char sentence[100];
while (cin.getline(sentence, 100))
cout << capitalizeFirstLetter(sentence) << '\n';
}
string capitalizeFirstLetter(string text) {
for (string::size_type i = 0; i < text.length(); i++) {
if (i == 0)
text[i] = toupper(text[i]);
if (text[i] == ' ')
if (++i < text.length())
text[i] = toupper(text[i]);
}
return text;
}
Sample Run :
Input :
hello world
foo bar
Output :
Hello World
Foo Bar
My Version (Requires C++20) :
#include <cctype>
#include <iostream>
#include <string>
auto capitalizeFirstLetter(std::string text) {
for (bool newWord = true; auto &&i : text) {
i = newWord ? std::toupper(i) : i;
newWord = std::isspace(i);
}
return text;
}
int main() {
std::string sentence;
while (std::getline(std::cin, sentence))
std::cout << capitalizeFirstLetter(sentence) << std::endl;
}
Sample Run
I am reading a file using fstream and getline functions. I want to give a starting position e.g. my file has 13 lines I want to start reading it from 7th line for example. Here is my code:
#include<iostream>
#include <stdlib.h>
#include <string>
#include <vector>
#include<iterator> // for iterators
#include<map>
using namespace std;
int main()
{
string line;
int start= 7;
unsigned long int index;
For( int z=1; z<=13; z++){
if (f_node.is_open())
{
getline(f_node, line);
if ((line.find("$EndNodes") != string::npos))
{
cout << "$EndNodes found file closed .... " << endl;
f_node.close();
return false;
}
// Point index.
int i = 0;
int j = line.find_first_of(" ", i);
index = strtoul((line.substr(i, j)).c_str(), NULL, 0);//
}
}
I am reading only indexes and I want to start it from 7th index How to do it?
To discard some number of lines, something like:
#include <fstream>
#include <string>
int main() {
std::ifstream infile{"myfile.txt"};
std::string line;
int starting_line = 7;
// Read and discard beginning lines
for (int n = 1; n < starting_line; n += 1) {
if (!std::getline(infile, line)) {
// Error or premature end of file! Handle appropriately.
}
}
while (std::getline(infile, line)) {
// Do something with the lines you care about.
}
return 0;
}
Except with actual error checking and handling and such.
"there is no way to tell code the starting position like seekg and tellg?" No. NL is just like any other character, it does not receive any special treatment.
You simply must scan the stream, counting the new-line character:
std::istream& seek_line(std::istream& is, const int n, std::ios_base::seekdir way = std::ios_base::beg)
{
is.seekg(0, way);
int i = 0;
char c;
while (is.get(c) && i < n)
if (c == '\n')
++i;
is.putback(c);
return is;
}
And this is how you use the above function:
int main()
{
using namespace std;
ifstream is{ "c:\\temp\\test.txt" };
if (!is)
return -1;
if (!seek_line(is, 3))
return -2;
string s;
getline(is, s);
cout << s << endl;
return 0;
}
I'm currently writting a program where I try to filter extra spaces so if there are more than 1 spaces in a row, I discard the rest leaving only one
But this is only the first step because the aim of the program is to parse a txt file with mips assembly instructions.
So far I've opened the file, stored the content in a vector and then stored the vector content in an array. Then I check, if you find a char 2 times in a row shift the array to the left.
The problem is that the code works well for any other letter, except for the space character. (On the code below I test it with the 'D' character and it works)
#include <iostream>
#include <cmath>
#include <fstream>
#include <cstdlib>
#include <vector>
#include <algorithm>
using namespace std;
class myFile {
vector<string> myVector;
public:
void FileOpening();
void file_filter();
};
void myFile::FileOpening() {
string getcontent;
ifstream openfile; //creating an object so we can open files
char filename[50];
int i = 0;
cout << "Enter the name of the file you wish to open: ";
cin.getline(filename, 50); //whatever name file the user enters, it's going to be stored in filename
openfile.open(filename); //opening the file with the object I created
if (!openfile.is_open()) //if the file is not opened, exit the program
{
cout << "File is not opened! Exiting the program.";
exit(EXIT_FAILURE);
};
while (!openfile.eof()) //as long as it's not the end of the file do..
{
getline(openfile, getcontent); //get the whole text line and store it in the getcontent variable
myVector.push_back(getcontent);
i++;
}
}
void myFile::file_filter() {
unsigned int i = 0, j = 0, flag = 0, NewLineSize, k, r;
string Arr[myVector.size()];
for (i = 0; i < myVector.size(); i++) {
Arr[i] = myVector[i];
}
//removing extra spaces,extra line change
for (i = 0; i < myVector.size(); i++) {
cout << "LINE SIZE" << myVector[i].size() << endl;
for (j = 0; j < myVector[i].size(); j++) {
//If I try with this character for example,
//it works (Meaning that it successfully discards extra 'Ds' leaving only one.
// But if I replace it with ' ', it won't work. It gets out of the loop as soon
//as it detects 2 consecutive spaces.
if ((Arr[i][j] == 'D') && (Arr[i][j + 1] == 'D')) {
for (k = j; k < myVector[i].size(); k++) {
Arr[i][k] = Arr[i][k + 1];
flag = 0;
j--;
}
}
}
}
for (i = 0; i < myVector.size(); i++) {
for (j = 0; j < myVector[i].size(); j++) //edw diapernw tin kathe entoli
{
cout << Arr[i][j];
}
}
}
int main() {
myFile myfile;
myfile.FileOpening();
myfile.file_filter();
}
My question is, why does it work with all the characters except the space one, and how do I fix this?
Thanks in advace.
Wow. Many lines of code. I can only recomend to learn more about the STL and algorithms.
You can read the complete file into a vector using the vectors "range"-constructor and std::istream_iterator. Then you can replace one or more spaces in a string by using a std::regex. This is really not complicated.
In the below example, I do all the work, with 2 lines of code in function main. Please have a look:
#include <iostream>
#include <vector>
#include <iterator>
#include <algorithm>
#include <string>
#include <fstream>
#include <regex>
using LineBasedTextFile = std::vector<std::string>;
class CompleteLine { // Proxy for the input Iterator
public:
// Overload extractor. Read a complete line
friend std::istream& operator>>(std::istream& is, CompleteLine& cl) { std::getline(is, cl.completeLine); return is; }
// Cast the type 'CompleteLine' to std::string
operator std::string() const { return completeLine; }
protected:
// Temporary to hold the read string
std::string completeLine{};
};
int main()
{
// Open the input file
std::ifstream inputFile("r:\\input.txt");
if (inputFile)
{
// This vector will hold all lines of the file. Read the complete file into the vector through its range constructor
LineBasedTextFile text{ std::istream_iterator<CompleteLine>(inputFile), std::istream_iterator<CompleteLine>() };
// Replace all "more-than-one" spaces by one space
std::for_each(text.begin(), text.end(), [](std::string& s) { s = std::regex_replace(s, std::regex("[\\ ]+"), " "); });
// For Debug purposes. Print Result to std::out
std::copy(text.begin(), text.end(), std::ostream_iterator<std::string>(std::cout, "\n"));
}
return 0;
}
I hope, I could give you some idea on how to proceed.
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
}
}