I'm making an OpenGL game in C++. I'm fairly inexperinced in C++ as opposed to other languages. Anyway, I create a stringstream with the "base" directory for some images. I then pass this stringstream as a function parameter to a constructor. The constructor appends an image file name, then attempts to load the resulting path. However...
D:\CodeBlocks Projects\SnakeRoid\bin\Debug\Texts\ <-- before appending the filename
Ship01.tgacks Projects\SnakeRoid\bin\Debug\Texts\ <-- After.
Obviously not correct! The result should be D:\CodeBlocks Projects\SnakeRoid\bin\Debug\Texts\Ship01.tga
The relevant parts of my code:
std::stringstream concat;
std::string txtFullPath = "Path here";
...
concat.str(""); //Reset value (because it was changed in ...)
concat << texFullPath; //Restore the base path
PS = new PlayerShip(&TexMan, concat); //Call the constructor
The constructor's code
PlayerShip::PlayerShip(TextureManager * TexMan, std::stringstream &path)
{
texId = 2;
std::cout << path.str(); //First path above
path << "Ship01.tga";
std::cout << path.str(); //Second - this is the messed up one
//Do more fun stuff
}
Anyone have any idea why its "overwriting" what's already in the stringstream?
why its "overwriting" what's already in the stringstream
Because output places characters at the "put pointer" position in the output buffer. A freshly-constructed stream has the put pointer set to zero (except for file output streams opened in append mode), thus your output overwrites the characters already in the buffer.
If you really need to append strings this way, you need to move the put pointer to the end of the buffer:
std::cout << p.str(); //First path above
std::stringstream path;
path.str(p.str());
path.seekp(0, std::ios_base::end); // <-- add this
path << "Ship01.tga";
std::cout << "Loading player ship from " << path.str();
EDIT: The question has been edited and the code after the edit works, because it no longer uses path.str(p.str()); to create the output buffer without using an output operation (and without advancing the put pointer): see ideone for differences.
In any case, strings themselves can be concatenated, which would make the code easier to follow:
std::string p = path.str() + "Ship01.tga";
std::cout << p;
Not to mention that for dealing with files and pathnames, we have boost.filesystem.
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I am trying to add data into a text file. However, i see for some reason it produces garbage data. I also notice, it will input the correct data once, but then it follow with garbage data.
void TextFileLogger::log(std::string msg){
using namespace std;
//ofstream output_file("students.data", ios::binary);
std::ofstream logFile;
// creating, opening and writing/appending data to a file
char filename[] = "log.txt";
logFile.open(filename, ios::binary | ios::app |ios::out);
if (logFile.fail())
{
std::cout << "The " << filename << " file could not be created/opened!" << std::endl;
// 0-normal, non zero - some errors
}
else
{
if (!logFile.write((char*)&msg, sizeof(msg)))
{
cout << "Could not write file" << endl;
}
else
{
streamsize bytesWritten = logFile.tellp();
if (bytesWritten != sizeof(msg))
{
cout << "Could not write expected number of bytes" << endl;
}
else
{
logFile << msg << std::endl;
cout << "file written OK" << endl;
}
}
}
}
That one is fun!
(char*)&msg does not do what you expect: std::string is mainly a pointer to a dynamically-allocated buffer which contains the actual data. When you take the std::string's address and try to read what's inside, you get a view of its innards, not its data. Using a C++ static_cast here would have spared you the trouble by telling you that the conversion makes no sense. sizeof(msg) similarly returns the size of the std::string, not the length of its data.
So, your solution is: use msg.data() and msg.size(), it's exactly what they're designed for.
But... why would it (sometimes) output your string, and a bunch of garbage? Well, std::strings typically use SSO (Small String Optimization). The std::string actually contains a small buffer, to store short enough strings without dynamic allocation. When you inspect the whole std::string object, you see this buffer pass by.
You are writing the contents of the whole std::string object, with all the member variables that it contains internally.
You either want:
logFile << msg;
or if you really want to use write():
logFile.write( msg.c_str(), msg.length());
And, I wonder: Why do create/open the file in binary mode, when you write strings afterwards?
And finally, you write the data twice, the second time in your last else clause.
The problem is with this line:
if (!logFile.write((char*)&msg, sizeof(msg)))
It should be this:
if (!logFile.write(msg.c_str(), msg.length()))
Since you are passing a std::string into the function, you should take advantage of the functions it provides (c_str() and length()) instead of trying to cast it to a char* (this always gets messy, plus you are casting away the const, which is also typically bad).
This:
if (!logFile.write((char*)&msg, sizeof(msg)))
is wrong in so many ways. msg is not an array of char, it's a std::string - lying to the compiler by using a cast is always a bad thing to do. And the size of a string is not the size of the characters it contains. Why the heck are you not using the obvios:
logfile << msg << std::endl;
Replace sizeof(msg) with msg.size(), sizeof() is not doing what you think!
Also (char*)&msg does not do whatever you think, use msg.data() instead.
logFile.write((char*)&msg, sizeof(msg));
should be rewritten to:
logFile.write(msg.data(), msg.size());
or, even better, because ofstream overrides operator<< for std::string:
logfile << msg;
I am facing a strange issue with my application, and although I have tried several solutions, none have solved my problem.
My c++ application generates a set of files with custom data. So far, the code seems to work fine, and the files are generated correctly, except the first one. The expected format of the files is the following:
#Header
#Line1E1,Line1E2,Line1E3
#Line2E1,Line2E2,Line1E3
However, I have noticed a strange empty space on the first line of the first generated file (and only the first one):
#Header
#Line1E1,Line1E2,Line1E3
#Line2E1,Line2E2,Line1E3
Since the code is the same for all the files, I am wondering what dit it go wrong, but so far I have not been able to detect the root of my problem.
The following is a simplified version of my code:
/* Variables */
std::ofstream Fil;
std::stringstream ss;
ss.precision (10);
ss.width (10);
ss.setf (ios::fixed);
for (int Inx = 0; Inx < MaxInx; Inx++) {
sprintf (FilNam, "%i-ExportFile.txt", Inx);
Fil.open(std::string (FilNam).c_str (), std::ofstream::out);
SavSta = Fil.is_open ();
if (SavSta) {
ss << "#Header" << "\n";
ss << "#Matrix name: " << MtxName << "\n";
ss << /* Matrix data goes here */ << "\n";
Fil << ss.rdbuf ();
ss.str(std::string ());
ss.clear ();
}
Fil.close ();
}
It is coming from :
ss.width(10);
From cplusplus.com
If the standard width of the representation is shorter than the field width, the representation is padded with fill characters
Just remove it and you'll be OK.
Hi I have some C++ code that uses user defined input to generate file-names for some output files:
std::string outputName = fileName;
for(int i = 0; i < 4; i++)
{
outputName.pop_back();
}
std::string outputName1 = outputName;
std::string outputName2 = outputName;
outputName.append(".fasta");
outputName1.append("_Ploid1.fasta");
outputName2.append("_Ploid2.fasta");
Where fileName could be any word the user can define with .csv after it e.g. '~/Desktop/mytest.csv'
The code chomps .csv off and makes three filenames / paths for 3 output streams.
It then creates them and attempts to open them:
std::ofstream outputFile;
outputFile.open(outputName.c_str());
std::ofstream outputFile1;
outputFile1.open(outputName1.c_str());
std::ofstream outputFile2;
outputFile2.open(outputName2.c_str());
I made sure to pass the names to open as const char* with the c_str method, however if I test my code by adding the following line:
std::cout << outputFile.is_open() << " " << outputFile1.is_open() << " " << outputFile2.is_open() << std::endl;
and compiling and setting fineName as "test.csv". I successfully compile and run, however,
Three zeros's are printed to screen showing the three filestreams for output are not in fact open. Why are they not opening? I know passing strings as filenames does not work which is why I thought conversion with c_str() would be sufficient.
Thanks,
Ben W.
Your issue is likely to be due to the path beginning with ~, which isn't expanded to /{home,Users}/${LOGNAME}.
ifstream open file C++
This answer to How to create a folder in the home directory? may be of use to you.
Unfortunately, there is no standard, portable way of finding out exactly why open() failed:
Detecting reason for failure to open an ofstream when fail() is true
I know passing strings as filenames does not work which is why I thought conversion with c_str() would be sufficient.
std::basic_ofstream::open() does accept a const std::string & (since C++11)!
I'm trying to store strings directly into a file to be read later in C++ (basically for the full scope I'm trying to store an object array with string variables in a file, and those string variables will be read through something like object[0].string). However, everytime I try to read the string variables the system gives me a jumbled up error. The following codes are a basic part of what I'm trying.
#include <iostream>
#include <fstream>
using namespace std;
/*
//this is run first to create the file and store the string
int main(){
string reed;
reed = "sees";
ofstream ofs("filrsee.txt", ios::out|ios::binary);
ofs.write(reinterpret_cast<char*>(&reed), sizeof(reed));
ofs.close();
}*/
//this is run after that to open the file and read the string
int main(){
string ghhh;
ifstream ifs("filrsee.txt", ios::in|ios::binary);
ifs.read(reinterpret_cast<char*>(&ghhh), sizeof(ghhh));
cout<<ghhh;
ifs.close();
return 0;
}
The second part is where things go haywire when I try to read it.
Sorry if it's been asked before, I've taken a look around for similar questions but most of them are a bit different from what I'm trying to do or I don't really understand what they're trying to do (still quite new to this).
What am I doing wrong?
You are reading from a file and trying to put the data in the string structure itself, overwriting it, which is plain wrong.
As it can be verified at http://www.cplusplus.com/reference/iostream/istream/read/ , the types you used were wrong, and you know it because you had to force the std::string into a char * using a reinterpret_cast.
C++ Hint: using a reinterpret_cast in C++ is (almost) always a sign you did something wrong.
Why is it so complicated to read a file?
A long time ago, reading a file was easy. In some Basic-like language, you used the function LOAD, and voilà!, you had your file.
So why can't we do it now?
Because you don't know what's in a file.
It could be a string.
It could be a serialized array of structs with raw data dumped from memory.
It could even be a live stream, that is, a file which is appended continuously (a log file, the stdin, whatever).
You could want to read the data word by word
... or line by line...
Or the file is so large it doesn't fit in a string, so you want to read it by parts.
etc..
The more generic solution is to read the file (thus, in C++, a fstream), byte per byte using the function get (see http://www.cplusplus.com/reference/iostream/istream/get/), and do yourself the operation to transform it into the type you expect, and stopping at EOF.
The std::isteam interface have all the functions you need to read the file in different ways (see http://www.cplusplus.com/reference/iostream/istream/), and even then, there is an additional non-member function for the std::string to read a file until a delimiter is found (usually "\n", but it could be anything, see http://www.cplusplus.com/reference/string/getline/)
But I want a "load" function for a std::string!!!
Ok, I get it.
We assume that what you put in the file is the content of a std::string, but keeping it compatible with a C-style string, that is, the \0 character marks the end of the string (if not, we would need to load the file until reaching the EOF).
And we assume you want the whole file content fully loaded once the function loadFile returns.
So, here's the loadFile function:
#include <iostream>
#include <fstream>
#include <string>
bool loadFile(const std::string & p_name, std::string & p_content)
{
// We create the file object, saying I want to read it
std::fstream file(p_name.c_str(), std::fstream::in) ;
// We verify if the file was successfully opened
if(file.is_open())
{
// We use the standard getline function to read the file into
// a std::string, stoping only at "\0"
std::getline(file, p_content, '\0') ;
// We return the success of the operation
return ! file.bad() ;
}
// The file was not successfully opened, so returning false
return false ;
}
If you are using a C++11 enabled compiler, you can add this overloaded function, which will cost you nothing (while in C++03, baring optimizations, it could have cost you a temporary object):
std::string loadFile(const std::string & p_name)
{
std::string content ;
loadFile(p_name, content) ;
return content ;
}
Now, for completeness' sake, I wrote the corresponding saveFile function:
bool saveFile(const std::string & p_name, const std::string & p_content)
{
std::fstream file(p_name.c_str(), std::fstream::out) ;
if(file.is_open())
{
file.write(p_content.c_str(), p_content.length()) ;
return ! file.bad() ;
}
return false ;
}
And here, the "main" I used to test those functions:
int main()
{
const std::string name(".//myFile.txt") ;
const std::string content("AAA BBB CCC\nDDD EEE FFF\n\n") ;
{
const bool success = saveFile(name, content) ;
std::cout << "saveFile(\"" << name << "\", \"" << content << "\")\n\n"
<< "result is: " << success << "\n" ;
}
{
std::string myContent ;
const bool success = loadFile(name, myContent) ;
std::cout << "loadFile(\"" << name << "\", \"" << content << "\")\n\n"
<< "result is: " << success << "\n"
<< "content is: [" << myContent << "]\n"
<< "content ok is: " << (myContent == content)<< "\n" ;
}
}
More?
If you want to do more than that, then you will need to explore the C++ IOStreams library API, at http://www.cplusplus.com/reference/iostream/
You can't use std::istream::read() to read into a std::string object. What you could do is to determine the size of the file, create a string of suitable size, and read the data into the string's character array:
std::string str;
std::ifstream file("whatever");
std::string::size_type size = determine_size_of(file);
str.resize(size);
file.read(&str[0], size);
The tricky bit is determining the size the string should have. Given that the character sequence may get translated while reading, e.g., because line end sequences are transformed, this pretty much amounts to reading the string in the general case. Thus, I would recommend against doing it this way. Instead, I would read the string using something like this:
std::string str;
std::ifstream file("whatever");
if (std::getline(file, str, '\0')) {
...
}
This works OK for text strings and is about as fast as it gets on most systems. If the file can contain null characters, e.g., because it contains binary data, this doesn't quite work. If this is the case, I'd use an intermediate std::ostringstream:
std::ostringstream out;
std::ifstream file("whatever");
out << file.rdbuf();
std::string str = out.str();
A string object is not a mere char array, the line
ifs.read(reinterpret_cast<char*>(&ghhh), sizeof(ghhh));
is probably the root of your problems.
try applying the following changes:
char[BUFF_LEN] ghhh;
....
ifs.read(ghhh, BUFF_LEN);
I'm making an OpenGL game in C++. I'm fairly inexperinced in C++ as opposed to other languages. Anyway, I create a stringstream with the "base" directory for some images. I then pass this stringstream as a function parameter to a constructor. The constructor appends an image file name, then attempts to load the resulting path. However...
D:\CodeBlocks Projects\SnakeRoid\bin\Debug\Texts\ <-- before appending the filename
Ship01.tgacks Projects\SnakeRoid\bin\Debug\Texts\ <-- After.
Obviously not correct! The result should be D:\CodeBlocks Projects\SnakeRoid\bin\Debug\Texts\Ship01.tga
The relevant parts of my code:
std::stringstream concat;
std::string txtFullPath = "Path here";
...
concat.str(""); //Reset value (because it was changed in ...)
concat << texFullPath; //Restore the base path
PS = new PlayerShip(&TexMan, concat); //Call the constructor
The constructor's code
PlayerShip::PlayerShip(TextureManager * TexMan, std::stringstream &path)
{
texId = 2;
std::cout << path.str(); //First path above
path << "Ship01.tga";
std::cout << path.str(); //Second - this is the messed up one
//Do more fun stuff
}
Anyone have any idea why its "overwriting" what's already in the stringstream?
why its "overwriting" what's already in the stringstream
Because output places characters at the "put pointer" position in the output buffer. A freshly-constructed stream has the put pointer set to zero (except for file output streams opened in append mode), thus your output overwrites the characters already in the buffer.
If you really need to append strings this way, you need to move the put pointer to the end of the buffer:
std::cout << p.str(); //First path above
std::stringstream path;
path.str(p.str());
path.seekp(0, std::ios_base::end); // <-- add this
path << "Ship01.tga";
std::cout << "Loading player ship from " << path.str();
EDIT: The question has been edited and the code after the edit works, because it no longer uses path.str(p.str()); to create the output buffer without using an output operation (and without advancing the put pointer): see ideone for differences.
In any case, strings themselves can be concatenated, which would make the code easier to follow:
std::string p = path.str() + "Ship01.tga";
std::cout << p;
Not to mention that for dealing with files and pathnames, we have boost.filesystem.