Hey guys I'm new to this,
I managed to make c++ open a random .jpg file from a folder using srand, the files are named sequentially 1-25.
Now I want to print out which file has been chosen by the randomizer every time I run the programm and log it into a .txt file.
The log in the .txt file should look like this:
4
8
5
..and so on, so that it adds the result of the randomizer to a new line each time it gets executed.
This is the code I have so far:
#include <sstream>
#include <string>
#include <cstdlib>
#include <ctime>
#include <fstream>
using namespace std;
int main()
{
srand((unsigned)time(0));
ostringstream oss;
oss << "\"C:\\Users\\etc..";
oss << rand() % 25 + 1;
oss << ".jpg\"";
system(oss.str().c_str());
system("pause");
return 0;
}
See below a complete example how you can achieve what you described.
The function LogToFile uses std::ofstream to open a file in append mode, and write to it.
You can change it if you'd like a different format (e.g. separate by commas instead of newline).
In order to call it with the number I added a variable n to hold the number (rather than streaming it directly into the std::ostringstream).
A side note: better to avoid using namespace std - see here Why is "using namespace std;" considered bad practice?.
The code:
#include <string>
#include <ctime>
#include <fstream>
#include <sstream>
#include <assert.h>
bool LogToFile(std::string const & filename, int n)
{
std::ofstream file;
file.open(filename, std::ios_base::app); // open in append mode
if (!file.is_open())
{
return false;
}
file << n << std::endl;
file.close();
return true;
}
int main()
{
// change according to your needs:
const std::string LOG_FILENAME = "log.txt";
const std::string IMAGE_FOLDER = "C:\\tmp";
srand((unsigned)time(0));
int n = rand() % 25 + 1;
// Add the number to the log file:
bool bRes = LogToFile(LOG_FILENAME, n);
assert(bRes);
std::ostringstream oss;
oss << "\"" << IMAGE_FOLDER << "\\" << n << ".jpg" << "\"";
system(oss.str().c_str());
system("pause");
return 0;
}
Related
i'm trying to write a script in c++ which read a CSV file so i can treat it later .i ve used fstram but the file always fail to open**
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main(){
string filename = "hello.txt"; // could come from command line.
ifstream fin(filename.c_str());
if (!fin.is_open())
{
cout << "Could not open file: " << filename << endl;
return 1;
}
cout<<"khalil"<<endl;
string scores[32];
string names[32];
int iter = 0;
while (iter <= 5)
{
fin >> names[iter] >> scores[iter];
cout << iter <<"\n";
cout<<names[iter]<< "\n";
cout<<scores[iter]<<"\n";
iter++;
}
fin.close();
}
Try using a fully qualified path name, e.g.:
string filename = "C:\\Documents\\hello.txt";It appears your program isn't opening the file because it can't find it.
You can use QFile class to do this operation.
#include <QFile>
#include <QStringList>
#include <QDebug>
int main()
{
QFile file("C\\hello.txt");
if (!file.open(QIODevice::ReadOnly)) {
qDebug()<<file.errorString();
return 0;
}
QStringList firstList, secondList;
while (!file.atEnd()) {
QByteArray line = file.readLine();
firstList.append(line.split(',')[0]);
secondList.append(line.split(',')[1]);
}
qDebug()<<firstList;
qDebug()<<secondList;
}
In my program I use an external function which generates output to me and I don't want it not to be generated by that function alone,
it's possible?
int main()
{
int a;
//I don't want the output of this function
a = function();
//now i want output
cout << "the result is : " << a;
}
Is it possible?
EDIT:
The function is in an external library.
Using only standard C++ where no dup-like functions exist, you could open a temporary std::FILE and std::swap with stdout.
#include <cerrno>
#include <cstring>
#include <cstdio>
#include <fstream>
#include <iostream>
#include <iterator>
#include <string>
#include <sstream>
// extern "C" int function(); // an assumption
// A helper class to temporarilly redirect the output to stdout to a file and to read
// the content of the file afterwards.
class BufferStdout {
public:
// the collector string is used for collecting the output to stdout
BufferStdout (std::string& collector) :
m_collector(collector),
fp(std::fopen("output.txt", "w"))
{
if(fp == nullptr) throw std::runtime_error(std::strerror(errno));
std::swap(stdout, fp); // swap stdout and the temp file
}
~BufferStdout () {
std::swap(stdout, fp); // swap back
std::fclose(fp);
// read the content of the temp file into m_collector
if(std::ifstream is("output.txt"); is) {
m_collector.append(std::istreambuf_iterator<char>(is),
std::istreambuf_iterator<char>{});
}
std::remove("output.txt"); // cleanup
}
private:
std::string& m_collector;
std::FILE* fp;
};
int main() {
std::string collector; // the string that will contain the output from function()
int a;
{
BufferStdout foo(collector);
a = function();
}
std::cout << "the result is : " << a << '\n';
std::cout << "Collected from function():\n";
std::cout << collector << '\n';
}
Yes it is generally possible but a bit complicated, a similar question is in Suppress output to cout from linked library
In addition to you can redirect stdout before invoking the shared library function and then redirect it again after the use of the shared library function in the however this is also a suboptimal solution. Best solution would be to adapt the shared library
// Cpp program to redirect cout to a file
#include <fstream>
#include <iostream>
#include <string>
using namespace std;
int main()
{
fstream file;
file.open("cout.txt", ios::out);
string line;
// Backup streambuffers of cout
streambuf* stream_buffer_cout = cout.rdbuf();
streambuf* stream_buffer_cin = cin.rdbuf();
// Get the streambuffer of the file
streambuf* stream_buffer_file = file.rdbuf();
// Redirect cout to file
cout.rdbuf(stream_buffer_file);
cout << "This line written to file" << endl;
// Redirect cout back to screen
cout.rdbuf(stream_buffer_cout);
cout << "This line is written to screen" << endl;
file.close();
return 0;
}
Note: The above steps can be condensed into a single step
auto cout_buf = cout.rdbuf(file.rdbuf())
// sets couts streambuffer and returns the old
streambuffer back to cout_buf
source : https://www.geeksforgeeks.org/io-redirection-c/
use
fclose(stdout);
with this function you will suppress any printf inside your libraries.
Of course you can not print other stuff inside your software.
I am trying to print the data located in the weapon.obj file, but it's not working.
Compiler Error: error: no matching function for call to
'getline(std::ifstream&)'|
Code:
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
ofstream render_weapon_OBJ ("weapon.obj");
render_weapon_OBJ << ("Weapon Names");
render_weapon_OBJ.close();
ifstream execute_weapon_OBJ ("weapon.obj");
while (getline(execute_weapon_OBJ))
{
cout << execute_weapon_OBJ << '\n';
}
execute_weapon_OBJ.close();
}
You must specify where to read the data and use that for printing.
#include <iostream>
#include <fstream>
#include <string> // add this to use std::string
using namespace std;
int main()
{
ofstream render_weapon_OBJ ("weapon.obj");
render_weapon_OBJ << ("Weapon Names");
render_weapon_OBJ.close();
ifstream execute_weapon_OBJ ("weapon.obj");
string weapon; // add this for read buffer
while (getline(execute_weapon_OBJ, weapon)) // add where to read
{
cout << weapon << '\n'; // print what was read instead of the stream
}
execute_weapon_OBJ.close();
}
May be this is the solution you are looking for
You need a variable to store the line read from the file and you need to print the variable not the variable used to initialize the file stream.
The error is in the while loop[The new code is below]
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
string line;
ofstream render_weapon_OBJ ("weapon.obj");
render_weapon_OBJ << ("Weapon Names");
render_weapon_OBJ.close();
ifstream execute_weapon_OBJ ("weapon.obj");
while(getline(execute_weapon_OBJ,line))
{
cout << line << '\n';
}
execute_weapon_OBJ.close();
}
Lets start with that I have absolutely no experience with C++ , but I got this project to connect a POS with a verifone. We do not have the standard verifone SDK but something custom.
At fist I needed to prepair data to send to C++ and C++ will send it to the Verifone. This is where I am getting stuck, I have a .txt file, which I can read with C++ but now I need to split the data.
This is my current code:
#include "stdafx.h"
#include <sstream>
#include <iostream>
#include <fstream>
#include <vector>
using namespace std;
string file_get_contents(const char *filename)
{
ifstream in(filename);
if (in.fail())
{
cerr << "File not found: " << filename << endl;
return "";
}
std::stringstream buffer;
buffer << in.rdbuf();
in.close();
return buffer.str();
}
int main(int argc, char **argv)
{
vector<string> strings;
string contents = file_get_contents("C:/wamp/www/cmd/config.txt");
string s;
while (contents, s, '||') {
cout << s << endl;
strings.push_back(s);
}
cout << s; // ECHO CONTENTS
std::cin.ignore(); // pause
return 0;
}
With this code my console just stays blank, no data is being displayed.
The full string I am splitting is:
"notepad://amount=10320.53||session_id=7946548443287465/"
The result that I want is to get an array that uses "amount" and "session_id" as keys and their values as value.
What is the best way of achieving this?
I used the following code to actually display the string in my console which was working:
int main(int argc, char **argv)
{
string contents = file_get_contents("config.txt");
cout << contents; // ECHO CONTENTS
std::cin.ignore(); // pause
return 0;
}
This shows how to use a regex to extract the information you want, there are a lot of online resources on how to read files properly so I left that part out.
#include <iostream>
#include <regex>
#include <unordered_map>
#include <string>
int main(int argc, char **argv)
{
std::regex pattern("amount=([[:digit:]\\.]*)\\|\\|session_id=([[:digit:]]*)");
std::smatch results;
std::unordered_map<std::string, std::string> data;
std::string contents = "notepad://amount=10320.53||session_id=7946548443287465/";
//string contents = file_get_contents("C:/wamp/www/cmd/file.txt");
if(std::regex_search(contents, results, pattern))
{
data["amount"] = results[1];
data["session_id"] = results[2];
}
std::cout << "Amount: " << data["amount"] << std::endl;
std::cout << "Seesion ID: " << data["session_id"] << std::endl;
return 0;
}
Basically I need to open and read a list of files I get from another command.
For each line of output of popen
open a file usen ifstream.open
it compiles and if I put the file name directly it works fine, but it doesn't do anything when using popen output. I've seen questions like this but none of this particular way of giving filenames.
here's the code:
#include <iostream>
#include <sqlite3.h>
#include <stdio.h>
#include <fstream>
using namespace std;
int main () {
ifstream singlefile;
FILE *filelist;
char filename[512];
string progline;
if(!(filelist = popen("find `pwd` -name \"*.js\"", "r"))){
return 1;
}
while( fgets(filename, sizeof(filename), filelist)!=NULL)
{
cout << filename;
singlefile.open(filename, ifstream::in);
while ( singlefile.good() )
{
getline (singlefile,progline);
cout << progline << endl;
}
singlefile.close();
}
pclose(filelist);
return 0;
}
next step would be not open each file inside the loop but to store the file list and then open each file.
Thanks
fgets keeps the trailing newline, resulting in a filename of a non-existing file. Also the stream state is only updated after reading. If I replace the while body with the following code, it works for me:
cout << filename;
size_t len = strlen(filename);
// chop off trailing newline
if (len > 1 && filename[len - 1] == '\n') filename[len - 1] = 0;
singlefile.open(filename, ifstream::in);
while ( getline(singlefile, progline) )
{
cout << progline << endl;
}
singlefile.close();
If you actually want to iterate through a list of files, I'd use Boost.Filesystem, which has a nice C++ interface, works for all filenames (even for those with newlines), and is platform-independent.
If this actually is only an example and your actual command is not find, there is still some room for simplification. Here is a suggestion that uses Boost.Iostreams to get rid of most of the C function calls (it would be great to have a device source reading from a process's standard output, but Boost.Iostreams lacks that):
#include <cstdio>
#include <iostream>
#include <fstream>
#include <stdexcept>
#include <string>
#include <stdio.h>
#include <boost/noncopyable.hpp>
#include <boost/iostreams/stream.hpp>
#include <boost/iostreams/device/file_descriptor.hpp>
using namespace std;
namespace io = boost::iostreams;
class Popen: private boost::noncopyable {
public:
explicit Popen(const char* command):
m_stream(popen(command, "r")) {
if (!m_stream) throw runtime_error("popen failed");
}
~Popen() {
pclose(m_stream);
}
FILE* stream() const {
return m_stream;
}
private:
FILE* m_stream;
};
int main() {
Popen pipe_wrapper("find `pwd` -name \"*.cpp\"");
io::file_descriptor_source pipe_device(fileno(pipe_wrapper.stream()), io::never_close_handle);
io::stream<io::file_descriptor_source> pipe_stream(pipe_device, 0x1000, 0x1000);
string filename;
while (getline(pipe_stream, filename)) {
cout << filename << endl;
ifstream file_stream(filename.c_str(), ifstream::in);
string progline;
while (getline(file_stream, progline)) {
cout << progline << endl;
}
}
}