I am currently doing an assignment in C++ in which I have to load a bunch of data from a .txt
file into a linked list:
Here is my load code:
void record::load( string fileName ) throw( recordException )
{
ifstream inFile( fileName.c_str() );
string c;
string t;
double p;
int q;
node *tail;
while (!isEmpty())
{
remove( 1 );
}
size = 0;
if ( getline(inFile, c) ||getline(inFile,t)||inFile >> p>> q) // Is file empty?
{ // File not empty:
try
{
head = new node;
// Add the first integer to the list.
head->cat = c;
head->title = t;
head->price = p;
head->qty = q;
head->next = NULL;
tail = head;
size = size + 1;
inFile.skipws;
// Add remaining items to linked list.
while ( getline(inFile, c)||getline(inFile ,t)||inFile >> p>> q)
// while(inFile.getline(c,50)||inFile.getline(t,50)||inFile>>p>>q)
{
tail->next = new node;
tail = tail->next;
tail->cat = c;
tail->title = t;
tail->price = p;
tail->qty = q;
tail->next = NULL;
size = size + 1;
inFile.skipws;
} // end while
} // end try
catch (bad_alloc e)
{
throw recordException(
"recordException: restore cannot allocate memory.");
} // end catch
} // end if
inFile.close();
}
It works great, except for one issue: I get really weird numbers when I try to display the data that is loaded in my linked list.
This is what it looks like when my program runs:
Can anyone help me? What can I do to remove those numbers? Why do these numbers occur anyway?
I am using C++ Codeblocks 16.01, if that is of any help.
Next time, don't use images, always copy/paste the actual text into your post instead.
Your reading code does not match the format of your input data. When you call getline()
, it reads until it encounters a line break or EOF.
So, the first call to getline(inFile, c)
reads the ENTIRE first line in one go:
" DVD Snow White 20 20"
Then getline(inFile,t)
reads the NEXT line in one go:
" VCD Cinderella 10 10"
Then inFile >> p >> q
tries to parse the NEXT line and fails:
" MT Wonderworld 20 30"
Since MT
is not a double
and Wonderworld
is not an int
.
You need to read the file line-by-line, parsing each line individually, for example:
#include <string>
#include <sstream>
void record::load( std::string fileName ) throw( recordException )
{
while (!isEmpty())
remove( 1 );
size = 0;
std::ifstream inFile( fileName.c_str() );
if (!inFile.is_open())
return;
std::string line;
std::string c;
char t[25+1] = {0}; // <-- use whatever your max title length actually is...
double p;
int q;
node *newNode;
while (std::getline(inFile, line)) // Is file empty?
{
std::istringstream iss(line);
if ((iss >> c) && iss.get(t, sizeof(t)) && (iss >> p >> qty))
{
try
{
newNode = new node;
newNode->cat = c;
newNode->title = t;
newNode->price = p;
newNode->qty = q;
newNode->next = NULL;
if (!head)
head = newNode;
if (tail)
tail->next = newNode;
tail = newNode;
++size;
}
catch (const bad_alloc &e)
{
throw recordException(
"recordException: restore cannot allocate memory.");
}
}
}
}
Regular Expression is much more suitable for task like this. You can use something like:
std::string test = " DVD Snow White 20 20";
std::regex re("\\s*(\\S+)\\s+(\\S.*\\S)\\s+(\\d+)\\s+(\\d+)");
std::smatch match;
if (std::regex_match(test, match, re)) {
for (size_t i = 0; i < match.size(); ++i) {
std::cout << "submatch " << i << ": \"" << match[i] << "\"\n";
}
}
So you could read file line by line and split it using that RE:
std::regex re("\\s*(\\S+)\\s+(\\S.*\\S)\\s+(\\d+)\\s+(\\d+)");
std::string line;
while( std::getline( inFile, line ) ) {
std::smatch match;
if (!std::regex_match(test, match, re)) continue;
std::string cat = match[1].str();
std::string title = match[2].str();
double price = std::stod( match[3].str() );
int qty = std::stoi( match[4].str() );
// you insert your node into list here
}
Note: I made RE pattern based on your input - price contains only digits, no dot. If it is not the case you would need to modify RE accordingly.
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