In a small utility I'm writing, I want to read a file record and:
look for the presence of an XOR checksum in the form *XX, where XX are hex digits
replace it if it's incorrect
add one if it's not present
So far, I'm only to the point of reading the file and looking for the checksum. The problem I'm up against is that std::string::find is not finding the * I know to be present; it returns npos every time.
The find() is on line 37. The first line read into strInput is:
$GPGGA,14240.99,2732.581,S,15301.947,E,1,06,3,65,M,37,M,-1.0,0006*6E\n
Here's the code:
#include <iostream>
#include <string>
int main()
{
std::cout << "Enter input file name:\n";
std::string strFileName = "";
std::getline(std::cin, strFileName);
std::cout << "Filename entered: " << strFileName << '\n';
FILE* fp;
int nErrCode = EXIT_FAILURE;
fopen_s(&fp, strFileName.c_str(), "r+");
if (!fp)
{
std::string strErr = "Failed to open " + strFileName;
perror(strErr.c_str());
return nErrCode;
}
rewind(fp);
std::string strInput;
strInput.reserve(100);
std::string::size_type n;
do
{
fgets(&strInput[0], 99, fp);
std::cout << strInput.c_str();
//n = 0;
n = strInput.find('*');
if (n != std::string::npos)
std::cout << "Found checksum at position " << n;
else
std::cout << "Did not find checksum";
} while (!feof(fp));
}
Thanks in advance.
I've debugged this and all is well up to the find(). At that point, I can see that the return value is npos, even though I can see the value of strInput and verify that it contains an asterisk.
Related
Is it possible to edit a .mm file before it gets compiled in AppCenter?
In an attempt to fix a build error, I want to find and replace a string in ../node_modules/react-native/React/CxxBridge/RCTCxxBridge.mm.
I tried using sed -i 's/oldString/newString/g' ../node_modules/react-native/React/CxxBridge/RCTCxxBridge.mm inside appcenter-pre-build.sh but it does not work.
Any help will be appreciated,
Thanks.
Not sure if this is your case, but I needed to update a version number on a complex project. To replace the counter of the current version with a new one, I considered updating the file with each build. After some versions of bash scripts, I realized that it's easier for me to write a console application in C with a couple of parameters to solve this problem. Works almost perfect for me. If you need I can share the simple code of this program.
Here is the C code that looks for a string in the file passed as a parameter and replaces the version number in it.
int main(int argc, char* argv[])
{
cout << "Version changer start\n";
if (argc < 2) {
cout << "There is no path argument. Version was no changed.";
return 1;
}
string sourcePath = argv[1];
string targetPath = sourcePath + ".tmp";
bool firstLine = true;
cout << sourcePath << endl;
ifstream sourceFile(sourcePath); // open file for input
ofstream targetFile(targetPath); // open file for output
string line;
while (getline(sourceFile, line)) // for each line read from the file
{
// looking for the desired line
if (line.find("public static String VER") != std::string::npos) { // replace "public static String VER" to your string definition code
line.replace(0, 32, "");
line.replace(line.length() - 2, 2, "");
int number = atoi(line.c_str());
number++; // In my case, I get an integer and add one to it
string v = to_string(number);
line = " public static String VER = \"" + v + "\";";
cout << v;
}
if (firstLine) {
targetFile << line;
firstLine = false;
}
else
targetFile << endl << line;
}
sourceFile.close();
targetFile.close();
remove(sourcePath.c_str());
if (rename(targetPath.c_str(), sourcePath.c_str()) != 0)
perror("Error renaming file");
else
cout << endl << "----------- done -----------\n";
}
I'm new to coding in C and C++, and I have a program with
an issue. When I (try) to run it, it gives me this error:
"No suitable constructor exists to convert from "char" to "std::string".
I'm not sure what it means. My code is an example of a simple
substitution cipher covered in the book "Cracking Codes with Python" by Al Sweigart.
I just want to replicate it in C++. Here's my code:
#include <iostream> // for communicating with user
#include <string>
using namespace std;
string symbols = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; // all symbols
string encrypt(string msg, string key, string mode) {
string ca = symbols;
string cb = key;
string translated;
if (mode == "decrypt") {
ca, cb = cb, ca;
}
int index = 0;
for (index = 0; index < msg.length(); index++) {
cout << "index is " << index << endl;
int sindex = ca.find(msg[index]); // it works here
cout << "sindex is " << sindex << endl;
string cl = cb[sindex]; // the problem
translated += cl;
}
return translated;
}
int main() {
string msg = "";
string key = "";
string mode = "";
string ciphertext = ""; // our variables
cout << "Enter message: (no spaces please)\n";
cin >> msg;
cout << "Enter key (or \"none\" for using default):\n";
cin >> key;
if (key == "none") {
key = "QWERTYUIOPASDFGHJKLZXCVBNM";
}
cout << "Enter mode: (\"encrypt\" or \"decrypt\")\n";
cin >> mode;
ciphertext = encrypt(msg, key, mode);
cout << "The ciphertext is\n" << ciphertext;
}
For some reason it works with msg on line 17 but not with cb on line 19, even though
they're both std::string. The actual error is on line 19 with string cl = cb[sindex];.
Not even sure what's wrong. It works on line 17 int sindex = ca.find(/*The thing here*/msg[index]);.
(Maybe my Visual Studio 2019 has gone nuts.) If I replace cb with msg it still gives me the
same error. Maybe line 17 is a lucky line? Who knows? But please help, I'm so
confused!
I am trying to write a loop that validates user input, and then repeats if the input is bad. The input must be either a binary number (as a string) or a decimal number (as an int). I have seperate functions to validate this input, but they are not causing any trouble.
The problem arises when I select 1 or 2, and then willingly enter an invalid binary or decimal number. At this point, the do-while loop repeats successfully. The program prints another request for user input to cout, But when it comes time for the user to enter input, the program thinks that there is input in the console before I even enter anything. I believe this is a problem with whitespace/control characters in the buffer, but I am not sure how to fix it. I have tried using std::cin >> std::ws to clear any straggling white space, but no luck.
#include <iostream>
#include <string>
#include <limits>
#include <stdlib.h>
#include <stdio.h>
#include <ctype.h>
using std::cout;
using std::cin;
using std::endl;
using std::numeric_limits;
using std::max;
using std::streamsize;
using std::string;
//int toDecimal;
//true is is binary
bool validateBinary(const string &binaryNumber){
for(int i = 0; i < binaryNumber.length(); i++){
if((binaryNumber[i] != 1) && (binaryNumber[i] != 0)){
return false;
}
}
return true;
}
//true if is decimal
bool validateDecimal(){
return cin;
}
int main() {
int conversionType = 0; //we initialize conversionType to a default value of 0 to ensure the copiler it will always have a value
bool isBinary = false;
bool isDecimal = false;
string binaryNumberInput;
int decimalNumberInput;
do {
if(conversionType == 0){
cout << "Enter 1 to convert binary to decimal," << endl;
cout << "2 to convert decimal to binary, " << endl;
cout << "or 3 to exit the program: ";
std::cin >> std::ws; //to clear any whitespace fron cin
cin >> conversionType; //upon a second iteration, this value is read in before a user input is given
}
if(!cin || (conversionType != 1 && conversionType != 2)){
cout << "Incorrect input." << endl;
cin.clear(); //clear the fail bit
cin.ignore(numeric_limits<streamsize>::max(), '\n'); //used to ignore not-numeric input
}
cout << "You have selected option " << conversionType << "." << endl;
if(conversionType == 1){
cout << "Please enter a binary number: ";
cin >> binaryNumberInput;
isBinary = validateBinary(binaryNumberInput);
if(!isBinary){
cout << "The numbered you entered is not a binary number!" << endl;
conversionType = 0;
}
}
if(conversionType == 2){
cout << "Please enter a decimal number: ";
cin >> decimalNumberInput;
isDecimal = validateDecimal(); //true if succeeded, meaning is a number
if(!isDecimal){
cout << "The numbered you entered is not a decimal number!" << endl;
conversionType = 0;
}
}
}
while((conversionType != 1 && conversionType != 2) || (isBinary == isDecimal));
return 0;
}
Rather than debug your current program you might want to consider using the standard library to simply things
#include <iostream>
#include <string>
#include <bitset>
#include <climits>
#include <limits>
template<typename T>
void get(T& value)
{
while (!(std::cin >> value)) {
std::cout << "Invalid input\n";
std::cin.clear();
std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
}
}
int main()
{
std::cout << "Enter 1 to convert binary to decimal,\n" <<
"2 to convert decimal to binary\n";
int option;
if (std::cin >> option) {
switch (option) {
case 1: {
std::bitset<CHAR_BIT * sizeof(unsigned long long)> bits;
get(bits);
std::cout << bits.to_ullong() << '\n';
break;
}
case 2: {
unsigned long long i;
get(i);
std::cout << std::bitset<CHAR_BIT * sizeof i>(i) << '\n';
break;
}
}
}
}
If you want this to loop you should be able to add it back in again easily enough.
Instruction for program:
Read the list of names from “names.txt” in the format “First Last”.
Sort the names based upon typical alphabetic order of peoples names based upon last name then first name.
Write the sorted list to a file called “sortednames.txt” in the format “Last, First”.
Here's my code: file data was stored in fullname array but now I am stuck on how to flip the first and last name in the array??
int main()
{
const int MAXNAMES = 100;
int value = 0;
string fullname[MAXNAMES];
ifstream inFile;
inFile.open("names.txt"); //open the file to excess the rainfall data
if (inFile.fail()) // testing the file
{
cout << "Error opening file. Please check that the file currently `enter code here`exist" << endl;
exit(1);
}
cout << "File successfully open" << endl;
while(!inFile.eof())
{
while(value < 100)
{
getline(inFile,fullname[value]);
value++;
}
}
return 0;
}
To flip the name around you could do the following:
string myString;
int spacePosition;
value = 0;
while(value < 100) {
myString = fullname[value];
spacePosition = myString.find(" ");
fullname[value] = myString.substr(spacePostion) + " " + myString.substr(0, spacePostion -1);
}
I am a beginner with C++. I have a new project at work where I have to learn it, so I'm trying some things just to test my understanding. For this problem, I'm trying to read a file and then print it on screen. Super simple, just trying to get good at it and understand the functions that I'm using. I copied some text from a MS Word document into a notepad (*.txt) file, and I'm trying to read this *.txt file. All of the text in the word document is bolded, but other than that there are no 'unusual' characters. Everything prints out on the screen as it appears in the document except the bolded " - " symbol. This character is printed as the "u" with a hat character ("so called extended ASCII" code 150). I try to print out the integer value of this character in my array (which should be 150) but I get -106. I realize this signed integer has the same bits as the unsigned integer 150. My question is how to get the output to say 150? Here's my code:
#include <iostream>
#include <fstream>
using namespace std;
int main() {
unsigned char* input1;
int input1size = 57;
ifstream file("hello_world2.txt",ios::binary | ios::ate);
if (file.is_open()){
int size;
size = (int) file.tellg();
cout <<"This file is " << size << " bytes." << endl;
file.seekg(0,ios::beg);
input1 = new unsigned char[input1size];
file.read(input1, input1size);
cout << "The first " << input1size <<" characters of this file are:" << endl<<endl;
for (int i=0; i<input1size; i++) {
cout << input1[i];
}
cout<<endl;
}
else {
cout <<"Unable to open file" << endl;
int paus;
cin>>paus;
return 0;
}
file.close();
int charcheck = 25;
int a=0;
int a1=0;
int a2=0;
unsigned int a3=0;
unsigned short int a4=0;
short int a5=0;
a = input1[charcheck];
a1 = input1[charcheck-1];
a2 = input1[charcheck+1];
a3 = input1[charcheck];
a4 = input1[charcheck];
a5 = input1[charcheck];
cout <<endl<<"ASCII code for char in input1[" << charcheck-1 <<"] is: " << a1 << endl;
cout <<endl<<"ASCII code for char in input1[" << charcheck <<"] is: " << a << endl;
cout <<endl<<"ASCII code for char in input1[" << charcheck+1 <<"] is: " << a2 << endl;
cout <<endl<<"ASCII code for char in input1[" << charcheck <<"] as unsigned int: " << a3 << endl;
cout <<endl<<"ASCII code for char in input1[" << charcheck <<"] as unsigned short int: " << a4 << endl;
cout <<endl<<"ASCII code for char in input1[" << charcheck <<"] as short int: " << a5 << endl;
int paus;
cin>>paus;
return 0;
}
Output for all this looks like:
This file is 80 bytes.
The first 57 characters of this file are:
STATUS REPORT
PERIOD 01 u 31 JUL 09
TASK 310: APPLIC
ASCII code for char in input1[24] is: 32
ASCII code for char in input1[25] is: -106
ASCII code for char in input1[26] is: 32
ASCII code for char in input1[25] as unsigned int: 4294967190
ASCII code for char in input1[25] as unsigned short int: 65430
ASCII code for char in input1[25] as short int: -106
So it appears "int a" is always read as signed. When I try to make "a" unsigned, it turns all the bits left of the eight bits for the char to 1's. Why is this? Sorry for the length of the question, just trying to be detailed. Thanks!
What you're dealing with is the sign-extension that takes place when the char is promoted to int when you assign it to one of your a? variables.
All the higher order bits must be set to 1 to keep it the same negative value as was in the smaller storage of the char.