[SOLVED] how to split string into an array/list of lines in C++?

rohedin · 06-04-2010, 06:24 PM

How can i split a string like this,

Code:

This is my first line.
This is my second line.
This is my third line.

into,

Code:

"This is my first line.", "This is my second line.", "This is my third line."

in C++.

i.e. split the code at every new line

Thanx in advance!

-Ben

Sergei Steshenko · 06-04-2010, 06:34 PM

Quote:

Originally Posted by rohedin

How can i split a string like this,

Code:

This is my first line.
This is my second line.
This is my third line.

into,

Code:

"This is my first line.", "This is my second line.", "This is my third line."

in C++.

i.e. split the code at every new line

Thanx in advance!

-Ben

Read

man fgets

and find its C++ counterpart, though it's not strictly necessary.

tuxdev · 06-04-2010, 07:03 PM

The (superior) C++ counterpart to fgets() is std::getline(std::istream &, std::string &). Unlike fgets(), std::getline will properly handle lines of any length for free.

Code:

std::ifstream file("filename");
std::string line;
while(std::getline(file, line)) {
   // whatever
}

rohedin · 06-05-2010, 05:18 AM

Quote:

Originally Posted by tuxdev

The (superior) C++ counterpart to fgets() is std::getline(std::istream &, std::string &). Unlike fgets(), std::getline will properly handle lines of any length for free.

Code:

std::ifstream file("filename");
std::string line;
while(std::getline(file, line)) {
   // whatever
}

Does std::getline() only work on files? Can it be used on strings?
e.g.

Code:

std::string text = " one \n two \n three";
std::string line;
while(std::getline(text, line)) {
   // whatever
}

If not... no big deal

would be nice tho

tuxdev · 06-05-2010, 10:00 AM

Use stringstreams:

Code:

std::istringstream stream(text);
std::string line;
while(std::getline(stream, line)) {
   // whatever
}

rohedin · 06-06-2010, 03:18 AM

Is there any way of putting those lines into an array without predefining the arrays length. The array must be changeable in size.

e.g.

Code:

std::istringstream stream(text);
std::string line;
while(std::getline(stream, line)) {
   array.append(line); //Or how ever else you would go
                       //about appending to a list.
}

Thanx

harry edwards · 06-06-2010, 03:30 AM

I would personally use string tokenizing in c This method will eradicate the need for an array.

posixculprit · 06-06-2010, 03:41 AM

http://www.cplusplus.com/reference/stl/

Harry Edwards: Care to prove that strtok() eradicates one's need for an array?

harry edwards · 06-06-2010, 04:24 AM

The example in the link does exactly that:

Code:

char *tok = strtok(szString, ",");
while (tok != NULL) {
  // Do something with the tok
  tok = strtok(NULL,",");
}

I've used this method several times. 'tok' holds the string which represents the current token, subsequent calls to strtok moves the tok pointer onto the next token. To me that's eradicating the need for an array, though, I may have misunderstood?

posixculprit · 06-06-2010, 04:48 AM

Unless I have missed something, the OP has not mentioned what he intends to do with the extracted "lines". We are only informed that he is looking for a method to obtain them. Assume his "actual" problem is to sort the lines in alphanumeric order, the following approach no longer fits, does it:

Code:

char *tok = strtok(szString, ",");
while (tok != NULL) {
  // Do something with the tok
  tok = strtok(NULL,",");
}

johnsfine · 06-06-2010, 06:24 AM

Quote:

Originally Posted by rohedin

Is there any way of putting those lines into an array without predefining the arrays length. The array must be changeable in size.

Use std::vector instead of an array.

rohedin · 06-06-2010, 10:54 AM

Quote:

Originally Posted by posixculprit

Unless I have missed something, the OP has not mentioned what he intends to do with the extracted "lines". We are only informed that he is looking for a method to obtain them. Assume his "actual" problem is to sort the lines in alphanumeric order, the following approach no longer fits, does it:

Code:

char *tok = strtok(szString, ",");
while (tok != NULL) {
  // Do something with the tok
  tok = strtok(NULL,",");
}

Sorry...

You have a valid point there.
What I want to do is insert a character at point x, y in the string. x being the number of characters into the line and y being the line the character is inserted into.

If you know a function that could do that for me it would be very helpful but I would learn a lot less