There are many features in C++ programs that must be ``balanced'' to be syntactically correct. For example, every ( must be balanced by a corresponding ). Similarly for {} and []. There are other (somewhat more complex) situations. • Block comments must be balanced. Each /* must be balanced by a */ The complication here is that the tokens being balanced are not composed of single characters. Moreover, the ``closing comment'' */ starts with a character that is used in other ways (pointers, multiplication). • Quotes must be balanced. This applies to single quotes and double quotes. The complication here is that all the material between the matching quotes can contain any characters. The characters between the quotes do not require balancing. For example, the string "This is a /* ' * quote" is legal, and the comment and single-quote need not be balanced. • Inline comments are not balanced. Anything that comes after a comment is ignored until you get to the end of the line that's read in. You must write these two functions with the exact same function signature (include case): void printFile(istream &dictfile); Prints the file with preceding line numbers for each line. bool balanceFile(istream &dictfile); Takes a file dictfile and prints the matching code elements. Returns true if the file is balanced, false otherwise. A stack provides the mechanism needed for the algorithm. Basically, whenever a closing symbol (such as }) is seen, it must match the nearest opening symbol of the same type (such as {). One important point: do not write a large main file. Your main file should simply get a file name, call a function to print the file with line numbers, and then call a balance-checking function. Your Program Your program prompts the user for the name of the C++ source file to test. If unable to open the file, the program issues an appropriate ``file not found'' error message, and exits. Before beginning the check, your program prints the file with line numbers. Every time your program pops the stack (to check for balance), it issues a message such as pair matching [ and ] As soon as a balance-error condition is found, the program issues a message such as unmatched { symbol at line 16 and exits. Hints 1. You don't have to implement the stack, you can use the Standard Template Library's implementation . 3. You can read a file character-by-character using the get method from fstream. 4. You can read a file line-by-line by using getline. 5. A file that you have read all the way to the end can be read again by doing 6. infile.clear(); 7. infile.seekg(0, inFile.beg); 8. If you read up on vectors you won't need to read through the file twice. 9. When you read the / character, it may be the opening of a comment (as in /* or //), or it may be the division operator. You will have to read the character after it to decide. If it's not the opening comment, you may want to put back the following character. You can use putback() to do this. 10. When you read the * character, it may be the closing of a comment (as in */), or it may be the multiplication operator or a pointer operation. Once again, you may want to use putback(). 11. The opening-comment ``symbol'' /* and the closing-comment ``symbol'' */ are composed of two characters. One choice for a single character to push for a comment symbol might be an otherwise unused symbol character (for example, the character c). 12. You may find it useful to define a lot of utility functions, here are some examples although depending on your implementation you may not need these particular ones: bool isOpeningBrace(int c) returns true if c is an opening brace, parenthesis, or bracket, false otherwise. bool opensBlockComment(...) returns true if c and the character following it in infile form the opening of a comment (i.e., slash-star). If so, the character following the slash (i.e., *) is eaten. Returns false otherwise and puts the character following the slash back in the ifstream. Sample Runs Here are some samples of the output generated by the program. Notice that the C++ source code does not have to be legal C++, it just has to meet balance conditions. The program begins by printing the file to be tested with line numbers. It then checks the balance and reports on the outcome. A Balanced Test Case Please enter filename for C++ code: good_balance.cpp 1 /* 2 good_balance.cpp 3 Test data for CS2 Project 3 4 5 Created: 24 October 1997 6 Modified: 6 October 2015 7 */ 8 9 #define FOO '"* /* */ foo' 10 #define BAR " /* ' " 11 12 int main(int argc, char * argv[]) 13 { 14 char c = {'a';} 15 y = 3; 16 z = 4; 17 x = y * z; 18 y = x / z; 19 cout << "Hello world\n"; // :) 20 } 21 pair matching /* and */ pair matching ' and ' pair matching " and " pair matching [ and ] pair matching ( and ) pair matching ' and ' pair matching { and } pair matching " and " pair matching { and } Balance is ok
There are many features in C++ programs that must be ``balanced'' to be syntactically
correct. For example, every ( must be balanced by a corresponding ). Similarly for {}
and []. There are other (somewhat more complex) situations.
• Block comments must be balanced. Each /* must be balanced by a */ The
complication here is that the tokens being balanced are not composed of single
characters. Moreover, the ``closing comment'' */ starts with a character that is
used in other ways (pointers, multiplication).
• Quotes must be balanced. This applies to single quotes and double quotes. The
complication here is that all the material between the matching quotes can
contain any characters. The characters between the quotes do not require
balancing. For example, the string "This is a /* ' * quote" is legal, and the
comment and single-quote need not be balanced.
• Inline comments are not balanced. Anything that comes after a comment is
ignored until you get to the end of the line that's read in.
You must write these two functions with the exact same function signature (include
case):
void printFile(istream &dictfile);
Prints the file with preceding line numbers for each line.
bool balanceFile(istream &dictfile);
Takes a file dictfile and prints the matching code elements. Returns true if the file is
balanced, false otherwise. A stack provides the
closing symbol (such as }) is seen, it must match the nearest opening symbol of the
same type (such as {). One important point: do not write a large main file. Your main file
should simply get a file name, call a function to print the file with line numbers, and then
call a balance-checking function.
Your Program
Your program prompts the user for the name of the C++ source file to test. If unable to
open the file, the program issues an appropriate ``file not found'' error message, and
exits. Before beginning the check, your program prints the file with line numbers. Every
time your program pops the stack (to check for balance), it issues a message such as
pair matching [ and ]
As soon as a balance-error condition is found, the program issues a message such as
unmatched { symbol at line 16
and exits.
Hints
1. You don't have to implement the stack, you can use the Standard Template
Library's implementation .
3. You can read a file character-by-character using the get method from fstream.
4. You can read a file line-by-line by using getline.
5. A file that you have read all the way to the end can be read again by doing
6. infile.clear();
7. infile.seekg(0, inFile.beg);
8. If you read up on
9. When you read the / character, it may be the opening of a comment (as in /* or //),
or it may be the division operator. You will have to read the character after it to
decide. If it's not the opening comment, you may want to put back the following
character. You can use putback() to do this.
10. When you read the * character, it may be the closing of a comment (as in */), or it
may be the multiplication operator or a pointer operation. Once again, you may
want to use putback().
11. The opening-comment ``symbol'' /* and the closing-comment ``symbol'' */ are
composed of two characters. One choice for a single character to push for a
comment symbol might be an otherwise unused symbol character (for example,
the character c).
12. You may find it useful to define a lot of utility functions, here are some examples
although depending on your implementation you may not need these particular
ones:
bool isOpeningBrace(int c)
returns true if c is an opening brace, parenthesis, or bracket, false otherwise.
bool opensBlockComment(...)
returns true if c and the character following it in infile form the opening of a
comment (i.e., slash-star). If so, the character following the slash (i.e., *) is eaten.
Returns false otherwise and puts the character following the slash back in the
ifstream.
Sample Runs
Here are some samples of the output generated by the program. Notice that the C++
source code does not have to be legal C++, it just has to meet balance conditions. The
program begins by printing the file to be tested with line numbers. It then checks the
balance and reports on the outcome.
A Balanced Test Case
Please enter filename for C++ code: good_balance.cpp
1 /*
2 good_balance.cpp
3 Test data for CS2 Project 3
4
5 Created: 24 October 1997
6 Modified: 6 October 2015
7 */
8
9 #define FOO '"* /* */ foo'
10 #define BAR " /* ' "
11
12 int main(int argc, char * argv[])
13 {
14 char c = {'a';}
15 y = 3;
16 z = 4;
17 x = y * z;
18 y = x / z;
19 cout << "Hello world\n"; // :)
20 }
21
pair matching /* and */
pair matching ' and '
pair matching " and "
pair matching [ and ]
pair matching ( and )
pair matching ' and '
pair matching { and }
pair matching " and "
pair matching { and }
Balance is ok
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