While reading a binary file using DJGPP on DOS this code hangs.
This happens when the fread call is made. If the call is removed then the program runs successfully.
The same code runs fine through Visual C++ 2008.
Has anyone experienced similar issues with djgpp ?
Am I missing out on something really simple ?
char x;
string Filename = "my.bin" ;
fp = fopen(Filename.c_str(),"rb");
if (fp == NULL)
{
cout << "File not found" << endl ;
}
if (fseek (fp, 0, SEEK_END) != 0)
{
cout <<"End of File can't be seeked";
return -1;
}
if ( (fileLength = ftell(fp)) == -1)
{
cout <<"Can't read current position of file";
return -1;
}
if (fseek (fp, 0, SEEK_SET) != 0)
{
cout <<"Beginning of File can't be seeked";
return -1;
}
if (fread(&x,sizeof(x),1,fp) != sizeof(x))
{
cout <<"file not read correctly";
return -1;
}
I don't see what 'fp' is. I just have to assume it's 'FILE * fp;'.
I don't see that you actually include < stdio.h >, and have to assume you do.
I don't see that you actually include < iostream > and declare 'using namespace std;', and have to assume you do.
I don't see what comes after the fread() call that could tell you if call succeeded.
Going through the process of actually reducing your faulty code to the absolute but complete minimum to reproduce the error is the first thing you should do when a piece of code has you dumbfounded.
It might (and usually does) turn out that the problem isn't even where you thought it is.
That being said, I'd try replacing
if (fread(&x,sizeof(x),1,fp) != sizeof(x))
{
cout <<"file not read correctly";
return -1;
}
with
int i;
if ( ( i = fgetc( fp ) ) == EOF )
{
perror( "File not read correctly" );
return -1;
}
x = (char) i;
cout << "Success, read '" << x << "'." << endl;
Using 'perror()' instead of homebrewn cout messages gives you additional information on the cause of any error. Using 'fgetc()' will show you that the file actually does contain what you think it does, and that your problems are not due to the somewhat uncommon use of fread() for a single byte.
Then report back.
fread takes a pointer as the first parameter. If you only have to read in one character, char x; is fine, but pass the address of x instead.
fread(&x,sizeof(x),1,fp) != sizeof(x)
and since sizeof char is always 1 (by definition) you can very well write:
fread(&x,1,1,fp) != 1
Related
I have created a pseudo terminal in C++ using the following code:
int main(int, char const *[])
{
int master, slave;
char name[1024];
char mode[] = "0777"; //I know this isn't good, it is for testing at the moment
int access;
int e = openpty(&master, &slave, &name[0], 0, 0);
if(0 > e) {
std::printf("Error: %s\n", strerror(errno));
return -1;
}
if( 0 != unlockpt(slave) )
{
perror("Slave Error");
}
access = strtol(mode, 0, 8);
if( 0 > chmod(name, access) )
{
perror("Permission Error");
}
//std::cout << "Master: " << master << std::endl;
std::printf("Slave PTY: %s\n", name);
int r;
prompt = "login: ";
while(true)
{
std::cout << prompt << std::flush;
r = read(master, &name[0], sizeof(name)-1);
checkInput(name);
name[r] = '\0';
std::printf("%s", &name[0]);
std::printf("\n");
}
close(slave);
close(master);
return 0;
}
It works pretty well in the sense that from another terminal, I can do:
printf 'username' > /dev/pts/x
and it will appear and be processed as it should.
My question is: when I try to use screen, nothing appears on the screen terminal. Then when I type, it comes through to my slave 1 character at a time.
Does anyone know why this is? Or how I can fix it.
I can provide more detail if required.
Thank you :)
Because you're not flushing the buffer after you use printf.
As pauls answer already suggest you need to flush the buffer.
To do so you can use the tcflush function.
The first argument is the int of the file descriptor and the second can be one of the following:
TCIFLUSH Flushes input data that has been received by the system but
not read by an application.
TCOFLUSH Flushes output data that has been written by an application
but not sent to the terminal.
TCIOFLUSH Flushes both input and output data.
For more information see: https://www.ibm.com/docs/en/zos/2.3.0?topic=functions-tcflush-flush-input-output-terminal
I've been beating my head against a wall with this one for a while. I'm only trying to make a simple application to read out the contents of a file. Here's some of the code:
errno_t error;
if ((error = fopen_s(&f, file, "r")) == 0) {
while (true) {
std::wcout << std::endl << "NEW RUN" << std::endl;
wchar_t content[4096];
if (fgetswc(content, 4096, f) == 4096) {
std::wcout << content;
std::wcout.flush();
}
else {
std::wcout << content;
std::wcout.flush();
break;
}
}
fclose(f);
std::wcout << "PLEASE PRINT THIS NOW";
system("pause");
return 0;
}
And the custom fgetswc function:
int fgetswc(wchar_t buffer[], int count, FILE * f) {
for (int i = 0; i < count; i = i + 1) {
wchar_t c = fgetwc(f);
if (c != WEOF) {
buffer[i] = c;
} else {
return i;
}
}
return count;
}
It reads the first 4096 bytes out of the file, but then subsequent std::wcout calls will not print out to the console I have. It reads the rest of the file and ends successfully, as I can see using breakpoints and the debugger. content gets filled up every iteration. I also attempted putting in debug statements, but even those don't get printed. Am I just doing something wrong? As far as I can tell there's no special characters in my file, it's just a log file.
std::wcout << content;
This is effectively calling std::wostream::operator<<(const wchar_t *). It doesn't know that content is not a ␀-terminated string. In fact, it can't possibly know that it has valid length 4096 in the first case and some amount less in the second case (you don't save the return value of fgetswc).
Hi I am trying to make a directory in windows with this code
header
#include <direct.h>
script
int main() {
string local = "C:/Program Files (x86)/Mail";
try
{
_mkdir (local.c_str ());
cout << "It is made?";
}
catch(invalid_argument& e)
{
cout << e.what () << " " << (char*) EEXIST;
if (e.what () == (char*) EEXIST) {
cout << e.what () << " " << (char*) EEXIST;
}
return;
}
}
The file is clearly not made, but it is also not making the error it should.
_mkdir won't throw an exception. (This is not python or boost, or any smart middleware)
Read the documentation you were referring to: it returns a value. 0 is OK, -1: error, ask why to errno
Don't ignore the return value. You probably have insufficient rights without UAC elevation to create the directory.
So I finally figured errno out, which for errno you need the <errno.h> header. The complete list of errno codes.
If you want to see what errno code something is throwing lets say
if (
_mkdir(((string)"C:/Program Files (x86)/Mail").c_str()) == 0 ||
errno == 17 /* this is the code for - File exists - */
){
// Do stuff
} else {
int errorCode = errno; // You need to save the code before anything else,
// because something else might change its value
cout << errorCode;
}
I am new at C/C++,
So basically I want to call an .exe file that displays 2 numbers and be able to grab those two numbers to use them in my code.
To call the .exe file I've used the system command, but I am still not able to grab those two numbers that are displayed by the .exe file
char *files = "MyPath\file.exe";
system (files);
I think this is better aproach:
Here you just create new process, and you read data that process gives you. I tested this on OS X 10.11 with .sh file and works like a charm. I think that this would probably work on Windows also.
FILE *fp = popen("path to exe","r");
if (fp == NULL)
{
std::cout << "Popen is null" << std::endl;
}else
{
char buff[100];
while ( fgets( buff, sizeof(buff), fp ) != NULL )
{
std::cout << buff;
}
}
You need to escapr back slashes in C++ string literals so:
// note the double "\\"
char* files = "MyPath\\file.exe";
Or just use forward slashes:
char* files = "MyPath/file.exe";
Its not very efficient but one thing you can to with std::system is redirect the output to a file and then read the file:
#include <cstdlib>
#include <fstream>
#include <iostream>
int main()
{
// redirect > the output to a file called output.txt
if(std::system("MyPath\\file.exe > output.txt") != 0)
{
std::cerr << "ERROR: calling system\n";
return 1; // error code
}
// open a file to the output data
std::ifstream ifs("output.txt");
if(!ifs.is_open())
{
std::cerr << "ERROR: opening output file\n";
return 1; // error code
}
int num1, num2;
if(!(ifs >> num1 >> num2))
{
std::cerr << "ERROR: reading numbers\n";
return 1; // error code
}
// do something with the numbers here
std::cout << "num1: " << num1 << '\n';
std::cout << "num2: " << num2 << '\n';
}
NOTE: (thnx #VermillionAzure)
Note that system doesn't always work everywhere because unicorn
environments. Also, shells can differ from each other, like cmd.exe
and bash. – VermillionAzure
When using std::system the results are platform dependant and not all shells will have redirection or use the same syntax or even exist!
The following C++ code is to read a txt file and then write the numbers of chars in each line and the number of all chars in the txt file.I use MS Visual Studio 2008.But something is wrong.Only the number of all chars is input into the txt files,but the numbers of each line are not input into the txt files.Now I cannot figure it out.Could someone give me some advice?Thanks a lot!
And my another question is what should I do to insert something in the middle of the txt file?
This is my Code:
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
fstream inOut("copy.txt",ios::in | ios::out | ios::app);
if (!inOut)
{
cerr << "ERROR:cannot open file!" << endl;
return -1;
}
int cnt = 0;
char ch;
inOut.seekg(0);
while(inOut.get(ch))
{
cout.put(ch);
++cnt;
if ('\n' == ch)
{
ios::pos_type mark = inOut.tellg();
if (!inOut)
{
cerr << "ERROR!" << endl;
return -1;
}
inOut << cnt;
inOut.put(' ');
inOut.seekg(mark);
}
}
inOut.clear();
inOut << cnt << endl;
cout << "[" << cnt << "]" << endl;
}
The txt file before running:
The txt file after running:
The result in command line:
I don't know fstream's very well, but I think you want to change the way you are doing this. You can think of a file as a contiguous piece of memory. Appending on the end is easy, but inserting in the middle can be problematic. In particular, if you do insert something, then your seekg might not be valid.
I would recommend three strategies:
Understand what is going on currently (try closing file before seekg and see if anything gets written by the inOut << cnt;)
Read from one file, write to a different file -- this will most likely be more efficient and less complicated than trying to modify the file in place.
Read from source file, store and modify in memory, write out modified buffer to original file. For large files, this might be less efficient than #2, but it means you don't need two files on disk.
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
fstream inOut("copy.txt",ios::in | ios::out | ios::app);
if (!inOut)
{
cerr << "ERROR:cannot open file!" << endl;
return -1;
}
int cnt = 0;
int cntline=0;
char ch;
inOut.seekg(0);
while(inOut.get(ch))
{
cout.put(ch);
//++cnt it include '\n' it should put behind of "if"
if ('\n' == ch)
{ ios::pos_type mark = inOut.tellg();
if (!inOut)
{
cerr << "ERROR!" << endl;
return -1;
}
cntline=cnt-cntline; //add it to account the number of chars of each line
inOut.seekg(0,ios::end); //here!!!!!!!!!!!!!!!!!!!!!!!!!!! add this , the resault is finally right! the reason it's down here.
inOut << cntline;
cntline=cnt; // and here! it can assure the number of the chars of each line be right!
inOut.put(' ');
inOut.seekg(mark);
}
else
{
++cnt; // it's here!
}
}
inOut.clear();
inOut << cnt << endl;
cout << "[" << cnt << "]" << endl;
}
inOut.seekg(0,ios::end)
i'am not sure it,but you can take it a reference.
you open file with "ios::app",so the VS 2008 only allows you to add text start from the end of file (it won't happened in vc 6.0).
if the file is :
it's compile by
vs 2008
when get the first '\n' the file pointer is pointing to'vs 2008'(yes,it just like the common pointer point the string ). and i debug it then find a value of the stream object named _Wrotesome .its value is false!
so i think the compiler think the file pointer point at o const sting.so you just can't write anything whis this position. so i add the code inOut.seekg(0,ios::end);.now you
can write anything you want to this text!
wish this can help you !
I don't know why do you choose std::fstream as your tool. If std::fstream is not asked or necessary, I would like to provide a example to solve your problem. Here's some limitation:
a. I read all the file into memory in one ReadFile operation. If your file is large, you may replace it with a loop.
b. I suppose your line separator is '\n'.
c. I add [line_count] before the '\n', which look like better.
here's my code.
#include "windows.h"
#include "sstream"
int _tmain(int argc, _TCHAR* argv[])
{
HANDLE hFile = ::CreateFile(L"C:\\Users\\wujian\\Desktop\\pingback - Copy.log", GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
if (hFile != INVALID_HANDLE_VALUE )
{
DWORD dwSize = ::GetFileSize(hFile, NULL);
if (dwSize)
{
char *pBuffer = new char[dwSize];
DWORD dwRead = 0;
::ReadFile(hFile, pBuffer, dwSize, &dwRead, NULL);
if (dwRead == dwSize)
{
std::stringstream ss;
int iPos = 0;
int iLine = 0;
while (iPos < dwSize)
{
if (pBuffer[iPos] == '\n')
{
ss << '[' << iLine << ']';
iLine = 0;
}
ss << pBuffer[iPos];
iPos ++, iLine ++;
}
ss << '[' << dwSize << ']';
::SetFilePointer(hFile, 0, NULL, FILE_BEGIN);
DWORD dwWrite = 0;
::WriteFile(hFile, ss.str().c_str(), ss.str().length(), &dwWrite, NULL;
}
::CloseHandle(hFile);
}
}
return 0;
}