Reading lines and columns with different separators from a text file - c++

Question

I am trying to write a function that reads in individual lines from a text file. Each line has two or three columns. I am want to know most elegant/clean approach for it. I am need the function to work with different separators (\t,\n,' ',',',';').
My approach works correctly except for different separators.
E.g. Input:
6
0 0
1 1
2 2
3 3
4 4
5 5
10
0 1 0.47
2 0 0.67
3 0 0.98
4 0 0.12
2 1 0.94
3 1 0.05
4 1 0.22
3 2 0.24
4 2 0.36
4 3 0.69
Pattern Input:
[total number of vertices]
[id-vertex][\separetor][name-vertex]
...
[total number of edges]
[id-vertex][\separator][id-neighbor][\separetor][weight]
...
*\separetor=\t|\n|' '|','|';'
My approach:
void readStream(istream& is, const char separator) {
uint n, m;
is >> n;
cout << n << endl;
string name;
uint vertexId, neighborId;
float weight;
while(!is.eof()) {
for(uint i = 0; i < n; i++) {
is >> vertexId >> name;
cout << vertexId;
cout << " " << name << endl;
}
is >> m;
cout << m << endl;
for(uint j = 0; j < n; j++) {
is >> vertexId >> neighborId >> weight;
cout << vertexId;
cout << " " << neighborId;
cout << " " << weight << endl;
}
break;
}
}
Overview:
Problem: Different separators.
Others elegantes solutions: In general, someone have other elegant/clean solutions to the problem?

Answer 1

You may use boost split it can split a string on multiple separators that you can specify.
std::string = line;
std::vector<std::string> parts;
boost::split(parts, line, boost::is_any_of("\t\n,; "));

Answer 2

If you are sure the separator is not white space, you can just throw them into a garbage string (e.g. separator in the case follow)
is >> vertexId >> separator >> neighborId >> separator >> weight;

Answer 3

The following code may be useful:
int t1,t2;
double t3;//global variables...
void parse_Vertex_Line(char *str)
{
int tmp=0;
char *p=str;
//extract the vertex-id
while(*p >='0' && *p <='9')
tmp = tmp*10 + *(p++) -'0';
t1=tmp;
tmp=0;
p++;
//now extract the vertex-name..
while(*p >='0' && *p <='9')
tmp = tmp*10 + *(p++) -'0';
t2=tmp;
return;
}
void parse_Edge_Line(char *str)
{
//extracting the first two numbers is just the same...
int tmp=0;
char *p=str;
//extract the first vertex-id
while(*p >='0' && *p <='9')
tmp = tmp*10 + *(p++) -'0';
t1=tmp;
tmp=0;
p++;
//now extract the second vertex-id..
while(*p >='0' && *p <='9')
tmp = tmp*10 + *(p++) -'0';
t2=tmp;
p++;
//but extracting a double value is a bit different...
//extract the weight...
int before_decimal=0, after_decimal=0;
while(*p!='.')
before_decimal = before_decimal*10 + *(p++) -'0';
p++;
int no_of_digits=0;
while(*p>='0' && *p<='9')
{
after_decimal = after_decimal*10 + *(p++) -'0';
no_of_digits++;
}
//assign it to the global double variable...
t3 = before_decimal + (after_decimal/pow(10.0, no_of_digits));
}
Now what you do is first get the number of vertices(n). Next read each of the n lines.
Calling the function parse_Vertex_Line each time. Then read the number of edges and similarly call parse_Edge_Line each time. Extract the values and Store them.
This code works for almost any delimiters. Hope this looks elegant to you.

Answer 4

You could use(Considering that your file will always be in the above mentioned format)
fstream file;
file.open("abc.txt",ios::in);
int numOfVertices;
string line;
getline(file, line);
numOfVertices = stoi(line);
vector<int> xCoord;
vector<int> yCoord;
while((--numOfVertices)>=0)
{
string line;
getline(file, line);
std::size_t prev = 0, pos;
pos = line.find_first_of(" ';", prev);
xCoord.push_back(stoi(line.substr(prev, pos-prev)));
prev = pos+1;
pos = line.find_first_of(" ';", prev); //considering some of the delimiters
yCoord.push_back(stoi(line.substr(prev, pos-prev)));
}
This is to add the vertices. Similarly you may extract the edges as well.

Answer 5

I modified my other posting for this scenario: Override istream operator >> and modify delimiter (The explanation for this is first variant of the accepted solution here for a possible implementation).
In general one way you could possibly deal with the unwanted separators is to turn them into spaces!
My approach enables the use of new delimiters for operations '>>' from istream:
struct delimiterIsSpace : ctype<char> {
delimiterIsSpace() : ctype<char>(get_table()) {}
static mask const* get_table() {
static mask rc[table_size];
rc[';'] = ctype_base::space;
rc[','] = ctype_base::space;
rc[' '] = ctype_base::space;
rc['\t'] = ctype_base::space;
rc['\n'] = ctype_base::space;
return &rc[0];
}
};
How to use:
cin.imbue(locale(cin.getloc(), new delimiterIsSpace));
for (int a, b; cin >> a >> b; ) {
cout << "a=" << a << " b=" << b << "\n";
}