I was trying to improve my reply to another question here How to cut the content of a string till a particular string or position? to use pointer arithmetic and std::substr so I ended up with the following
#include <iostream>
#include <string>
#include <cstring>
std::string getString(std::string fullString){
char string[80];
char* endString;
strcpy(string, fullString.c_str());
strtok(string, "|");
for(int i = 0; i < 4; i++){
endString = strtok(NULL, "|");
}
return fullString.substr(endString - string, std::string::npos);
}
int main( void ){
std::string str("{[(2015/11/30|01:07:53.357|-1227639088|DefaultThread|./src/Myprogram.cpp:564|int main(int, argv**))]} Server Starting....");
std::cout << getString(str) << std::endl;
return 0;
}
However that crashes with a segmentation fault error, if I change it to
#include <iostream>
#include <string>
#include <cstring>
std::string getString(std::string fullString){
char string[80];
char* endString;
strcpy(string, fullString.c_str());
strtok(string, "|");
for(int i = 0; i < 4; i++){
endString = strtok(NULL, "|");
}
std::cout << fullString.substr(endString - string, std::string::npos) << std::endl;
return fullString.substr(endString - string, std::string::npos);
}
int main( void ){
std::string str("{[(2015/11/30|01:07:53.357|-1227639088|DefaultThread|./src/Myprogram.cpp:564|int main(int, argv**))]} Server Starting....");
std::cout << getString(str) << std::endl;
return 0;
}
The program runs fine and the output is as expected
./src/Myprogram.cpp:564|int main(int, argv**))]} Server Starting....
./src/Myprogram.cpp:564|int main(int, argv**))]} Server Starting....
why does it crash on the first scenario?
Your input string is 120 bytes wide. Your C-string buffer is 80 bytes wide. Hrmm.
Use the find functions instead of this error-prone C nonsense!!
To get everything since the last |:
#include <iostream>
#include <string>
#include <stdexcept>
std::string getString(const std::string& fullString)
{
size_t pos = fullString.rfind('|');
if (pos == std::string::npos)
throw std::runtime_error("Could not find a '|'!");
return fullString.substr(pos+1);
}
int main()
{
std::string str("{[(2015/11/30|01:07:53.357|-1227639088|DefaultThread|./src/Myprogram.cpp:564|int main(int, argv**))]} Server Starting....");
std::cout << getString(str) << std::endl;
}
(live demo)
Adjust as needed to scan back for the 2nd, 3rd, 4th |.
Your program has undefined behaviour because the length of the string stored in str is greater than 80 characters. Thus in this statement
strcpy(string, fullString.c_str());
you overwrite memory beyond array string.
Moverover it is a bad approach to use C function strtok instead of member function find (or rfind) of class std::string.
Also it is not clear why exactly magic number 4 is used in the loop
for(int i = 0; i < 4; i++){
endString = strtok(NULL, "|");
}
Related
I am a beginner and I just need a bit of help on why I getline is showing an error:
this is what I have so far
#include <iostream>
#include <iomanip>
#include <cmath>
#include <fstream>
using namespace std;
const double TAX_RATE = 0.0825;
const int MAX_ITEMS = 1000;
const int MAX_TRANSACTIONS = 100;
int main(int argc, char const *argv[]){
string fname = "";
int itemCnt = 0, start = 0, end = 0;
int ids[MAX_ITEMS], qtys[MAX_ITEMS];
double costs[MAX_ITEMS], subtotals[MAX_TRANSACTIONS],
taxes[MAX_TRANSACTIONS], totals[MAX_TRANSACTIONS];
string names[MAX_ITEMS], paymentTypes[MAX_ITEMS], payments[MAX_ITEMS];
ifstream iFile;
if ( argc != 2 ) {
cout<<"usage: "<< argv[0]<< " <file name>" <<endl;
return 0;
} else {
iFile.open(argv[1]);
}
if (!iFile) {
cout<<"Error: Invalid file name"<<endl;
cin.clear();
}
while (!iFile.eof())
{
getline(iFile,str); //this isn't working
int commaLoc = str.find(',');
ids[itemCnt]= str.substr(0,commaLoc);
str = str.substr(commaLoc +1, str.length());
//string to int I'm not sure how to do I know its something with stoi() but not sure how to format it
}
return 0;
}
I am able to get the file to open but I'm not sure why getline isn't working it keeps saying something like
no instance of overload function
My csv file looks like:
1,Laptop,799.99,1,cash,1100
I need it to read the first number and because Its a string i don't know how to save it as an int
Multiple errors. First there is nothing called 'str' in your program. I will guess its just a string used as a temp buffer
do not do this (!File.eof) it doesnt do what you think.
while (iFile)
{
string str; <<<<<==== added
getline(iFile,str); //this isn't working <<<===is now
int commaLoc = str.find(',');
Next this line doesnt work because ids are ints and substring returns a string.
// ids[itemCnt]= str.substr(0,commaLoc);
ids[itemCnt]= stoi(str.substr(0,commaLoc)); <<<<==== fixed
str = str.substr(commaLoc +1, str.length());
}
I strongly recommend you use std::vector instead of c-style fixed size arrays. Takes 5 minutes to learn how to use them and they have huge benefits. If you must use fixed size arrays use std::array instead of c-style
You can read a string and try to convert it to a number in different ways. For example, since C++17, you can use from_chars. One of its overloads:
Receives a pair of begin and end char pointers, and an int variable,
tries to parse an int number, and
and returns the parsed number, together with a pointer to the first character that wasn't part of the match.
int i{};
auto [ptr, ec] = std::from_chars(str.data(), str.data() + str.size(), i);
if (ec == std::errc{}) { /* do something with i */} else { /* error */ }
[Demo]
Full code (using a istrinstream instead of a ifstream):
#include <charconv> // from_chars
#include <iomanip>
#include <iostream>
#include <sstream> // istringstream
#include <system_error> // errc
constinit const int MAX_ITEMS = 10;
int main() {
std::istringstream iss{
"1,Laptop,799.99,1,cash,1100\n"
"2,PC,688.88,2,card,1101\n"
"blah,Keyboard,39.00,3,cash,1102"
};
size_t itemCnt{};
int ids[MAX_ITEMS]{};
std::string str{};
while (std::getline(iss, str)) {
// Parse counter
int i{};
auto [ptr, ec] = std::from_chars(str.data(), str.data() + str.size(), i);
if (ec == std::errc{}) {
ids[itemCnt] = i;
// Remaining string
std::string remaining_string{ str.substr(ptr - str.data() + 1) };
std::cout << ids[itemCnt] << ", " << remaining_string << "\n";
}
else {
std::cout << "Error: invalid counter.\n";
}
++itemCnt;
}
}
// Outputs:
//
// 1, Laptop,799.99,1,cash,1100
// 2, PC,688.88,2,card,1101
// Error: invalid counter.
I'm a newbie in C++ learning the language and playing around. I wrote a piece of code which behavior I don't understand. Could someone explain why the code below prints out random junk and not the first character of the first string in the list (that is a).
#include <iostream>
#include <vector>
#include <string>
#include <cstdlib>
#include <ctime>
#include <climits>
#include <stdio.h>
char* str2char(std::string str)
{
char cset[str.size()+1]; // +1 for the null character
for(int i = 0; i < str.size(); i++)
{
cset[i] = str[i];
}
cset[str.size()] = '\0';
return cset;
}
int main (int argc, char * const argv[]) {
std::vector< std::string > ladontakadet;
ladontakadet.push_back("aabcbbca");
ladontakadet.push_back("abcdabcd");
ladontakadet.push_back("cbbdcdaa");
ladontakadet.push_back("aadcbdca");
ladontakadet.push_back("cccbaaab");
ladontakadet.push_back("dabccbaa");
ladontakadet.push_back("ccbdcbad");
ladontakadet.push_back("bdcbccad");
ladontakadet.push_back("ddcadccb");
ladontakadet.push_back("baccddaa");
std::string v = ladontakadet.at(0);
char *r;
r = str2char(v);
std::cout << r[0] << std::endl;
return 0;
}
Why is my returning garbage, when I'm expecting it to output a?
Thnx for any help!
P.S. The output of this code is random. It doesn't always print the same character..:S
It's because you return a pointer to a local variable, a local variable that goes out of scope when the function returns.
You are already using std::string for the argument, use it instead of the array and the return pointer.
If your aim is to pass the content of a std::string to a function modifying the content of a char*:
#include <iostream>
#include <vector>
void f(char* s) {
s[0] = 'H';
}
std::vector<char> to_vector(const std::string& s) {
return std::vector<char>(s.c_str(), s.c_str() + s.size() + 1);
}
int main(void)
{
std::string s = "_ello";
std::vector<char> t = to_vector(s);
f(t.data());
std::cout << t.data() << std::endl;
}
Your function is returning garbage because you're returning the address of a local variable which goes out of scope after your function returns. It should probably look like this:
char* str2char(const std::string &str)
{
char *const cset = new char[str.size() + 1]; // +1 for the null character
strcpy(cset, str.c_str());
return cset;
}
You will need to delete your variable r by doing delete[] r;. Ideally though you wouldn't be using raw pointers, and you would use std::string for everything, or wrap the char * in a std::unique_ptr.
I've written a simple function to count occurrences of a character in a string. The compiler is fine. However, as I try to run it, it produced a segmentation fault.
#include <iostream>
using namespace std;
// To count the number of occurences of x in p
// p is a С-style null-terminated string
int count_x(char* p, char x)
{
if (p == nullptr)
{
return 0;
}
// start the counter
int count = 0;
while (p != nullptr)
{
if (*p == x)
{
++count;
}
}
return count;
}
int main(int argc, char const *argv[])
{
char myString[] = "Hello";
cout << count_x(myString, 'l');
return 0;
}
There's two mistakes in your code:
You only ever look at the first character in the string.
The last character of a null terminated string is a null character. You're testing the pointer itself.
You need to use std::string
#include <string>
#include <algorithm>
#include <iostream>
int main()
{
std::string str = "Hello";
std::cout << std::count(str.begin(), str.end(), 'l');
}
Using if and while/do-while, my job is to print following user's inputs (string value) in reverse order.
For example:
input string value : "You are American"
output in reverse order : "American are You"
Is there any way to do this?
I have tried
string a;
cout << "enter a string: ";
getline(cin, a);
a = string ( a.rbegin(), a.rend() );
cout << a << endl;
return 0;
...but this would reverse the order of the words and spelling while spelling is not what I'm going for.
I also should be adding in if and while statements but do not have a clue how.
The algorithm is:
Reverse the whole string
Reverse the individual words
#include<iostream>
#include<algorithm>
using namespace std;
string reverseWords(string a)
{
reverse(a.begin(), a.end());
int s = 0;
int i = 0;
while(i < a.length())
{
if(a[i] == ' ')
{
reverse(a.begin() + s, a.begin() + i);
s = i + 1;
}
i++;
}
if(a[a.length() - 1] != ' ')
{
reverse(a.begin() + s, a.end());
}
return a;
}
Here is a C-based approach that will compile with a C++ compiler, which uses the stack to minimize creation of char * strings. With minimal work, this can be adapted to use C++ classes, as well as trivially replacing the various for loops with a do-while or while block.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_LINE_LENGTH 1000
#define MAX_WORD_LENGTH 80
void rev(char *str)
{
size_t str_length = strlen(str);
int str_idx;
char word_buffer[MAX_WORD_LENGTH] = {0};
int word_buffer_idx = 0;
for (str_idx = str_length - 1; str_idx >= 0; str_idx--)
word_buffer[word_buffer_idx++] = str[str_idx];
memcpy(str, word_buffer, word_buffer_idx);
str[word_buffer_idx] = '\0';
}
int main(int argc, char **argv)
{
char *line = NULL;
size_t line_length;
int line_idx;
char word_buffer[MAX_WORD_LENGTH] = {0};
int word_buffer_idx;
/* set up line buffer - we cast the result of malloc() because we're using C++ */
line = (char *) malloc (MAX_LINE_LENGTH + 1);
if (!line) {
fprintf(stderr, "ERROR: Could not allocate space for line buffer!\n");
return EXIT_FAILURE;
}
/* read in a line of characters from standard input */
getline(&line, &line_length, stdin);
/* replace newline with NUL character to correctly terminate 'line' */
for (line_idx = 0; line_idx < (int) line_length; line_idx++) {
if (line[line_idx] == '\n') {
line[line_idx] = '\0';
line_length = line_idx;
break;
}
}
/* put the reverse of a word into a buffer, else print the reverse of the word buffer if we encounter a space */
for (line_idx = line_length - 1, word_buffer_idx = 0; line_idx >= -1; line_idx--) {
if (line_idx == -1)
word_buffer[word_buffer_idx] = '\0', rev(word_buffer), fprintf(stdout, "%s\n", word_buffer);
else if (line[line_idx] == ' ')
word_buffer[word_buffer_idx] = '\0', rev(word_buffer), fprintf(stdout, "%s ", word_buffer), word_buffer_idx = 0;
else
word_buffer[word_buffer_idx++] = line[line_idx];
}
/* cleanup memory, to avoid leaks */
free(line);
return EXIT_SUCCESS;
}
To compile with a C++ compiler, and then use:
$ g++ -Wall test.c -o test
$ ./test
foo bar baz
baz bar foo
This example unpacks the input string one word at a time,
and builds an output string by concatenating in reverse order.
`
#include <iostream>
#include <sstream>
using namespace std;
int main()
{
string inp_str("I am British");
string out_str("");
string word_str;
istringstream iss( inp_str );
while (iss >> word_str) {
out_str = word_str + " " + out_str;
} // while (my_iss >> my_word)
cout << out_str << endl;
return 0;
} // main
`
This uses exactly one each of if and while.
#include <string>
#include <iostream>
#include <sstream>
void backwards(std::istream& in, std::ostream& out)
{
std::string word;
if (in >> word) // Read the frontmost word
{
backwards(in, out); // Output the rest of the input backwards...
out << word << " "; // ... and output the frontmost word at the back
}
}
int main()
{
std::string line;
while (getline(std::cin, line))
{
std::istringstream input(line);
backwards(input, std::cout);
std::cout << std::endl;
}
}
You might try this solution in getting a vector of string's using the ' ' (single space) character as a delimiter.
The next step would be to iterate over this vector backwards to generate the reverse string.
Here's what it might look like (split is the string splitting function from that post):
Edit 2: If you don't like vectors for whatever reason, you can use arrays (note that pointers can act as arrays). This example allocates a fixed size array on the heap, you may want to change this to say, double the size when the current word amount has reached a certain value.
Solution using an array instead of a vector:
#include <iostream>
#include <string>
using namespace std;
int getWords(string input, string ** output)
{
*output = new string[256]; // Assumes there will be a max of 256 words (can make this more dynamic if you want)
string currentWord;
int currentWordIndex = 0;
for(int i = 0; i <= input.length(); i++)
{
if(i == input.length() || input[i] == ' ') // We've found a space, so we've reached a new word
{
if(currentWord.length() > 0)
{
(*output)[currentWordIndex] = currentWord;
currentWordIndex++;
}
currentWord.clear();
}
else
{
currentWord.push_back(input[i]); // Add this character to the current word
}
}
return currentWordIndex; // returns the number of words
}
int main ()
{
std::string original, reverse;
std::getline(std::cin, original); // Get the input string
string * arrWords;
int size = getWords(original, &arrWords); // pass in the address of the arrWords array
int index = size - 1;
while(index >= 0)
{
reverse.append(arrWords[index]);
reverse.append(" ");
index--;
}
std::cout << reverse << std::endl;
return 0;
}
Edit: Added includes, main function, while loop format
#include <vector>
#include <string>
#include <iostream>
#include <sstream>
// From the post
std::vector<std::string> &split(const std::string &s, char delim, std::vector<std::string> &elems)
{
std::stringstream ss(s);
std::string item;
while(std::getline(ss, item, delim)) {
elems.push_back(item);
}
return elems;
}
std::vector<std::string> split(const std::string &s, char delim) {
std::vector<std::string> elems;
return split(s, delim, elems);
}
int main ()
{
std::string original, reverse;
std::cout << "Input a string: " << std::endl;
std::getline(std::cin, original); // Get the input string
std::vector<std::string> words = split(original, ' ');
std::vector<std::string>::reverse_iterator rit = words.rbegin();
while(rit != words.rend())
{
reverse.append(*rit);
reverse.append(" "); // add a space
rit++;
}
std::cout << reverse << std::endl;
return 0;
}
This code here uses string libraries to detect the blanks in the input stream and rewrite the output sentence accordingly
The algorithm is
1. Get the input stream using getline function to capture the spacecs. Initialize pos1 to zero.
2. Look for the first space in the input stream
3. If no space is found, the input stream is the output
4. Else, get the position of the first blank after pos1, i.e. pos2.
5. Save the sub-string bewteen pos1 and pos2 at the beginning of the output sentence; newSentence.
6. Pos1 is now at the first char after the blank.
7. Repeat 4, 5 and 6 untill no spaces left.
8. Add the last sub-string to at the beginning of the newSentence. –
#include <iostream>
#include <string>
using namespace std;
int main ()
{
string sentence;
string newSentence;
string::size_type pos1;
string::size_type pos2;
string::size_type len;
cout << "This sentence rewrites a sentence backward word by word\n"
"Hello world => world Hello"<<endl;
getline(cin, sentence);
pos1 = 0;
len = sentence.length();
pos2 = sentence.find(' ',pos1);
while (pos2 != string::npos)
{
newSentence = sentence.substr(pos1, pos2-pos1+1) + newSentence;
pos1 = pos2 + 1;
pos2 = sentence.find(' ',pos1);
}
newSentence = sentence.substr(pos1, len-pos1+1) + " " + newSentence;
cout << endl << newSentence <<endl;
return 0;
}
I know how to program in C# and VB but not have idea about how to use C++ and have to program a little exe to a barcode scanner that use C++ :(
In this moment I try to parse a scanned barcode that have multiple data sepparated with a "/", I find that exist a strtok function, tested it "manually" and worked ok but I not implemented yet a working function to call it correctly, what I have now:
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
int elemStr(char *str, char sep)
{
int cantElem;
unsigned ich;
cantElem = 0;
if (strlen(str) > 0) //at least 1 elem
cantElem++;
for (ich = 0; ich < strlen(str); ich++)
{
if (str[ich] == sep)
cantElem++;
}
return cantElem;
}
char* getElemStr(char *str, char sep[], int elem)
{
char *tempStr = NULL;
char *tok;
int currElem = 1;
// 1st data
strcpy( tempStr, str);
tok = strtok( tempStr, sep);
while( currElem != elem )
{
// Get next tokens:
tok = strtok( NULL, sep );
currElem++;
}
return tok;
}
void main( void )
{
char barcode[] = "710015733801Z/1/35";
char sep[] = "/";
char sep1 = sep[0];
char barcd[20];
char piezaChar[4];
int pieza;
char mtsChar[4];
int cantElem;
cantElem = elemStr(barcode, sep1 );
if (cantElem >= 1)
{
strcpy(barcd, getElemStr(barcode,sep,1) ); //pasa a str resultado;
printf("Cod: %s\n", barcd ); //STACK OVERFLOW HERE!
}
}
if I use strtok witout a function "getElemStr" it work ok but I try to use it on other places too.
Can I use strtok like this? You have a working example?
pd: I not have idea about pointers (sorry), good doc to learn about that?
Since you specifically asked about C++, I'm going to ignore your very c-style code and show you how to do this in C++:
#include <boost/algorithm/string.hpp>
#include <iostream>
#include <string>
#include <vector>
int main()
{
std::string barcode = "710015733801Z/1/35";
std::string sep = "/";
std::vector<std::string> v;
boost::split(v, barcode, boost::is_any_of(sep));
for(size_t i=0; i<v.size(); ++i)
std::cout << v[i] << '\n';
}
strtok destroys your original string. So i don't think it can be used with a char* that points to a static string. Static strings get copied to a read only portion of the executable.
Here is a C++ solution that doesn't use boost.
#include <string>
#include <sstream>
#include <iostream>
int main()
{
std::string barcode = "710015733801Z/1/35";
std::stringstream ss(barcode);
std::string elem;
while(std::getline(ss, elem, '/'))
{
//do something else meaningful with elem
std::cout << elem << std::endl;
}
return 0;
}
Output:
710015733801Z
1
35