In my main method,
int main()
{
char *words = (char *)"GETGETYETYET";
char *pattern = (char *)"GET";
return 0;
}
Instead of *words and *pattern being a predefined char set, I want to get user input, the user types in the name of a .txt file, and I want the strings in that .txt file to be stored as (char *).
How can I do this?
You don't.
Unless you want to deal with string allocations, deallocations, and ownerships, with buffer overruns and security problems, you just use std::string...
Like this:
#include <iostream>
#include <string>
int main() {
std::string a = "abcde";
std::string b;
getline(std::cin, b);
std::cout << a << ' ' << b;
return 0;
}
Suppose your strings are on the file x.txt, one per line:
#include <iostream>
#include <string>
#include <fstream>
int main() {
std::string line;
std::ifstream f("x.txt");
while( std::getline(f, line) )
std::cout << ' ' << line << '\n';
return 0;
}
The point here being that you really don't want to store things in char*...
Related
Is there any way to tell a stringstream to ignore a null terminating char and read a certain amount of chars anyway?
As you can see from this minimum example, even though the char array consists of 3 chars, the stringstream terminates at the second position:
#include <sstream>
#include <iostream>
using namespace std;
int main(int argc, char* argv[]) {
char test[3];
test[0] = '1';
test[1] = '\0';
test[2] = '2';
stringstream ss(test);
char c;
cout << "start" << endl;
while (ss.get(c)) {
cout << c << endl;
}
if (ss.eof()) {
cout << "eof" << endl;
}
}
$ ./a.out
start
1
eof
This question is not about stringstreams. The problem is you are implicitly constructing a std::string from a const char* for that stringstream constructor argument, and doing so using the overload that expects a C-string. So, naturally, you should expect C-string-like behaviour.
Instead you can form the argument using the std::string(const char*, std::size_t) constructor, or send the data to a default-constructed stringstream using .write.
In addition to the other answer explaining the underlying problem (creating a std::string from a char*), here's one (of many) ways around the problem, using std::string_literals:
#include <iostream>
#include <string>
#include <sstream>
int main(){
using namespace std::string_literals;
const std::string str_with_null = "1\0002"s;
std::stringstream ss(str_with_null);
char c;
while (ss.get(c)) {
std::cout << static_cast<int>(c) << '\n';
}
}
When run, this should print out:
49
0
50
I'm trying to convert a sentence from upper case to lowercase. I also write a code but I stopper when a space is appear. How can I fix this problem and convert the whole sentence? Here is my code
#include<iostream>
#include<cstring>
using namespace std;
int main()
{
char str[100];
cin>>str;
for(int i=0;i<strlen(str);i++)
{
if(str[i]>='A'&&str[i]<='Z')
{
str[i]=str[i]+32;
}
}
cout<<str<<endl;
return 0;
}
It's because of theinput operator >>, it breaks on space. If you want to read a whole line then use std::getline to read into a std::string instead.
Then read about the C++ standard algorithms, like for example std::transform. Also, std::tolower doesn't modify anything that's not an upper-case letter, so it's a good function to use.
The error is because operator>> delimites on spaces. The alternative is to use getline. See the following example:
#include <cstring>
#include <iostream>
#include <string>
int main() {
std::string s;
std::getline(std::cin, s);
std::cout << "Original string: " << s << std::endl;
if (!std::cin.fail()) {
const int len = strlen(s.c_str());
for (size_t i = 0; len > i; ++i) {
if ((s[i] >= 'A') && (s[i] <= 'Z'))
s[i] = s[i] - 'A' + 'a';
}
}
std::cout << "New string: " << s << std::endl;
return 0;
}
The reason input stops at whitespace is because formatted input is delimited by whitespace characters (among others). You will need unformatted I/O in order to extract the entire string into str. One way to do this is to use std::istream::getline:
std::cin.getline(str, 100, '\n');
It's also useful to check if the input succeeded by using gcount:
if (std::cin.getline(str, 100, '\n') && std::cin.gcount())
{
...
}
But in practice it's recommended that you use the standard string object std::string which holds a dynamic buffer. To extract the entire input you use std::getline:
std::string str;
if (std::getline(std::cin, str)
{
...
}
Here is one of the examples of doing it using transform function.
#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
int main()
{
string str;
if (getline(cin, str))
{
transform(str.begin(), str.end(), str.begin(), ptr_fun<int, int>(toupper));
}
cout << str << endl;
return 0;
}
I want to ask for word from the user and then convert the word from string to char using 'strcpy'. Then I want to determine the sum of the ascii codes for all of the letters in the word.
However, I am having difficulties. I don't understand exactly how I can do that. This is what I have been able to do so far.
#include <iostream>
#include <time.h>
#include <stdlib.h>
#include <string.h>
using namespace std;
int main()
{
string word;
cout << "Enter word: ";
getline(cin, word);
/*
char w[word];
strcpy(w,word.c_str());
int ('A');
cout<<char(65);
*/
return 0;
}
The commented part is where I have been trying to do the converting. I copied the code from a worksheet. Even if it did work, I don't know how, and what it all means.
Thanks for your help.
char w[word];
strcpy(w, word.c_str());
char w[word] is incorrect. The square brackets is for the size, which must be a constant integral expression. word is of type std::string, so this makes neither logical nor practical sense. Maybe you meant it as:
char w = word;
But that still won't work because word is a string, not a character. The correct code in this case is:
char* w = new char[word.size() + 1];
That is, you allocate the memory for w using a char*. Then you use word.size() + 1 to initialize heap-allocated memory amounting to those bytes. Don't forget for the obligatory delete[] when you're finished using w:
delete[] w;
However, note that using raw pointers and explicit new is not needed in this case. Your code can easily be cleaned up into the following:
#include <numeric>
int main ()
{
std::string word;
std::getline(std::cin, word);
int sum = std::accumulate(word.begin(), word.end(), 0); /*
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ */
std::cout << "The sum is: " << sum << std::endl;
}
You don't need to use strcpy() (or use a char * at all, for that matter), but this'll do your counting using a char pointer:
#include <iostream>
#include <string>
int main() {
std::string word;
std::cout << "Enter word: ";
std::cin >> word;
const char * cword = word.c_str();
int ascii_total = 0;
while ( *cword ) {
ascii_total += *cword++;
}
std::cout << "Sum of ASCII values of characters is: ";
std::cout << ascii_total << std::endl;
return 0;
}
Output:
paul#local:~/src/cpp/scratch$ ./asccount
Enter word: ABC
Sum of ASCII values of characters is: 198
paul#local:~/src/cpp/scratch$
If you really do want to use strcpy(), I'll leave it as an exercise to you to modify the above code.
Here's a better way to do it, just using std::string (and C++11, and obviously presuming your system uses the ASCII character set in the first place):
#include <iostream>
#include <string>
int main() {
std::string word;
std::cout << "Enter word: ";
std::cin >> word;
int ascii_total = 0;
for ( auto s : word ) {
ascii_total += s;
}
std::cout << "Sum of ASCII values of characters is: ";
std::cout << ascii_total << std::endl;
return 0;
}
How do I split an input string using getline(cin, input); to input the variable? I want to split it into a char array like this:
char[] = { // What goes here to make it read the input variable and split it into chars }
Is there any way to do this?
And what about y'all's new posts? Which one is best? Here is the caesar cipher code I need to modify to read the input variable and store its chars in a char array:
// Test Code ONLY
// Not A Commercial Program OR A Crypter
// THIS IS A TEXT CIPHERER
#include <windows.h>
#include <cstdlib>
#include <iostream>
#include <string.h>
#include <vector>
using namespace std;
int main()
{
string in;
string out;
char lower[25] = {a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z};
char upper[25] = {A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z};
char upcip[25] = {Z,Y,X,W,V,U,T,S,R,Q,P,O,N,M,L,K,J,I,H,G,F,E,D,C,B,A};
char locip[25] = {z,y,x,w,v,u,t,s,r,q,p,o,n,m,l,k,j,i,h,g,f,e,d,c,b,a};
cout << "Enter PlainText: ";
getline(cin, in);
// which sample goes here to read the input var char by char, then store the chars in order in a char array in your opinion?
return 0;
}
A string is already an array of chars:
for (std::string line; std::getline(std::cin, line); )
{
for (std::size_t i = 0, e = line.size(); i != e; ++i)
{
std::cout << "char[" << i << "] = '" << line[i] << "'\n";
}
}
string str;
std::getline(cin,str);
char* pArr = new char[str.size() + 1]; // add 1 for zero element which is the end of string
strcpy(pArr,str.c_str());
/*
some actions with pArr, for ex.
while(*pArr)
std::cout << *pArr; // output string on the screen
*/
// updated: release memory obtained from heap
delete [] pArr;
I'm trying to read from a file, and make a vector of all the words from the file. What I tried to do below is have the user input the filename, and then have the code open the file, and skip characters if they aren't alphanumeric, then input that to a file.
Right now it just closes immediately when I input the filename. Any idea what I could be doing wrong?
#include <vector>
#include <string>
#include <iostream>
#include <iomanip>
#include <fstream>
using namespace std;
int main()
{
string line; //for storing words
vector<string> words; //unspecified size vector
string whichbook;
cout << "Welcome to the book analysis program. Please input the filename of the book you would like to analyze: ";
cin >> whichbook;
cout << endl;
ifstream bookread;
//could be issue
//ofstream bookoutput("results.txt");
bookread.open(whichbook.c_str());
//assert(!bookread.fail());
if(bookread.is_open()){
while(bookread.good()){
getline(bookread, line);
cout << line;
while(isalnum(bookread)){
words.push_back(bookread);
}
}
}
cout << words[];
}
I think I'd do the job a bit differently. Since you want to ignore all but alphanumeric characters, I'd start by defining a locale that treats all other characters as white space:
struct digits_only: std::ctype<char> {
digits_only(): std::ctype<char>(get_table()) {}
static std::ctype_base::mask const* get_table() {
static std::vector<std::ctype_base::mask>
rc(std::ctype<char>::table_size,std::ctype_base::space);
std::fill(&rc['0'], &rc['9']+1, std::ctype_base::digit);
std::fill(&rc['a'], &rc['z']+1, std::ctype_base::lower);
std::fill(&rc['A'], &rc['Z']+1, std::ctype_base::upper);
return &rc[0];
}
};
That makes reading words/numbers from the stream quite trivial. For example:
int main() {
char const test[] = "This is a bunch=of-words and 2#numbers#4(with)stuff to\tseparate,them, I think.";
std::istringstream infile(test);
infile.imbue(std::locale(std::locale(), new digits_only));
std::copy(std::istream_iterator<std::string>(infile),
std::istream_iterator<std::string>(),
std::ostream_iterator<std::string>(std::cout, "\n"));
return 0;
}
For the moment, I've copied the words/numbers to standard output, but copying to a vector just means giving a different iterator to std::copy. For real use, we'd undoubtedly want to get the data from an std::ifstream as well, but (again) it's just a matter of supplying the correct iterator. Just open the file, imbue it with the locale, and read your words/numbers. All the punctuation, etc., will be ignored automatically.
The following would read every line, skip non-alpha numeric characters and add each line as an item to the output vector. You can adapt it so it outputs words instead of lines. I did not want to provide the entire solution, as this looks a bit like a homework problem.
#include <vector>
#include <sstream>
#include <string>
#include <iostream>
#include <iomanip>
#include <fstream>
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
string line; //for storing words
vector<string> words; //unspecified size vector
string whichbook;
cout << "Welcome to the book analysis program. Please input the filename of the book you would like to analyze: ";
cin >> whichbook;
cout << endl;
ifstream bookread;
//could be issue
//ofstream bookoutput("results.txt");
bookread.open(whichbook.c_str());
//assert(!bookread.fail());
if(bookread.is_open()){
while(!(bookread.eof())){
line = "";
getline(bookread, line);
string lineToAdd = "";
for(int i = 0 ; i < line.size(); ++i)
{
if(isalnum(line[i]) || line[i] == ' ')
{
if(line[i] == ' ')
lineToAdd.append(" ");
else
{ // just add the newly read character to the string 'lineToAdd'
stringstream ss;
string s;
ss << line[i];
ss >> s;
lineToAdd.append(s);
}
}
}
words.push_back(lineToAdd);
}
}
for(int i = 0 ; i < words.size(); ++i)
cout << words[i] + " ";
return 0;
}