C++ Programming HOW-TO

Al Dev (Alavoor Vasudevan) alavoor@yahoo.com

v8.0, 26 April 2000

This document discusses methods to avoid memory problems in C++ and also will help you to program properly in C++ language. The information in this document applies to all the operating sytems that is - Linux, MS DOS, Apple Macintosh OS, Windows 95/NT, OS/2, IBM OSes, VMS, Novell Netware, all flavors of Unix like Solaris, HPUX, AIX, SCO, Sinix, BSD, etc.. and to all other operating systems which support "C++" compiler (it means almost all the operating systems on this planet!).

1. Introduction

1.1 Problems facing the current C++ compilers
1.2 Which one "C", "C++" or Java ?

2. Download mychar

4. C++ Zap (Delete) command

5. Pointers are problems

6. Usage of my_malloc and my_free

7. Debug files

8. C++ Online-Docs

8.1 C++ Tutorials
8.2 C++ Coding Standards
8.3 C++ Quick-Reference
8.4 C++ Usenet Newsgroups

9. Memory Tools

10. Related URLs

11. Other Formats of this Document

12. Copyright

13. Appendix A example_mychar.cpp

14. Appendix B mychar.h

15. Appendix C mychar.cpp

16. Appendix D my_malloc.cpp

17. Appendix E my_malloc.h

18. Appendix F debug.h

19. Appendix G debug.cpp

20. Appendix H Makefile

1. Introduction

C++ is the most popular language and will be used for a long time in the future inspite of emergence of Java. C++ runs extremely fast and is in fact 20 to 30 times FASTER than Java. Java runs very slow because it is an byte-code-interpreted language running on top of "virtual engine". The memory management in Java is automated, so that programmers do not directly deal with memory allocations. This document attempts to automate the memory management in C++ to make it much more easy to use. A neat feature of Java is that memory allocations are taken care of automatically. This howto will enable "C++" to "compete/imitate" with Java language in memory management.

Because of manual memory allocations, debugging the C++ programs consumes a major portion of time. The information in this document will give you some better ideas and tips to reduce the debugging time.

1.1 Problems facing the current C++ compilers

Since C++ is super-set of C, it got all the bad features of "C" language.

For example, in "C" programming - memory leaks, memory overflows are very common due to usage of features like -

        Datatype  char * and char[]
        String functions like strcpy, strcat, strncpy, strncat, etc..
        Memory functions like malloc, realloc, strdup, etc..

The usage of char * and strcpy causes horrible memory problems due to "overflow", "fence past errors" or "memory leaks". The memory problems are extremely hard to debug and are very time consuming to fix and trouble-shoot. Memory problems bring down the productivity of programmers. This document helps in increasing the productivity of programmers via different methods addressed to solve the memory defects in "C++". Memory related bugs are very tough to crack, and even experienced programmers take several days, weeks or months to debug memory related problems. Many times memory bugs will be "hiding" in the code for several months and can cause unexpected program crashes!! The usage of char * is costing USA and Japan $2 billion every year in time lost in debugging and downtime of programs. If you use char * in C++ then it is a very costly affair especially if your programs have more than a million lines of code.

Hence, the following techniques are proposed to overcome the faults of "C" language.

It is proposed that C++ compilers should prevent the programmers from using the "char *" , "char[]" datatypes and functions like strcpy, strcat, strncpy, strncat. The datatypes like char *, char[] and functions like strcpy, strcat are evil and must be completetly BANNED from usage in C++!! The "char *" is like smallpox virus and it must be eradicated from this world!!

Instead of using char * and char[] all the C++ programmers MUST use the 'mychar class' which is given in this document and 'string class' included in the STDLIB. The 'mychar class' utilises the constructor and destructor to automate the memory management and also provides many functions like ltrim, substring, etc..

See also related 'string class' in the C++ compiler. The string class is part of the standard GNU C++ library and provides lot of string manipulation functions. The 'string class' and 'mychar class' can remove the need of char * datatype. Also, C++ programmers must be encouraged to use 'new', 'delete' features instead of using 'malloc' or 'free'.

The 'mychar class' does everything that char * or char [] does. It can completely replace char datatype. Plus added benefit is that programmers do not have to worry about the memory problems and memory allocation at all!!

The GNU C++ compiler MUST drop off the support of char *, char[] datatypes and in order to compile older programs using char datatype, the compiler should provide a additional option called "-fchar-datatype" to g++ command. Over the next 2 years all the C++ programs will use 'mychar class' and 'string class' and there will be no char * and char[]. The compiler should try to prevent bad programming practices!

1.2 Which one "C", "C++" or Java ?

It is recommended you do programming in object-oriented "C++" for all your application programming or general purpose programming. You can take full advantage of object oriented facilities of C++. The C++ compiler is lot more complex than "C" compiler and C++ programs may run bit slower than "C" programs. But compiler optimizer options like -O or -O3 can speed up C++.

Nowadays, "C" language is primarily used for "systems programming" to develop operating sytems, device drivers etc..

Java is platform independent language more suitable for developing GUI running inside web-browsers (Java applets) but runs very slow. Prefer to use web-server-side programming "Fast-CGI" with C++ and HTML, DHTML, XML to get better performance. Hence, the golden rule is "Web-server side programming use C++ and web-client side (browser) programming use Java applets". The reason is - the server-side OS is under your control and never changes and you will never know what the client side web-browser OS is. It can be Windows 95/98/NT/2000 or Linux, Apple Mac, OS/2, Solaris etc..

2. Download mychar

All the programs, examples are given in Appendix of this document. You can download as a single tar zip, the mychar class, libraries and example programs from

Go here and click on C++Programming howto.tar.gz file http://www.aldev.8m.com
Mirror site : http://aldev.webjump.com

3. Usage of mychar class

The 'mychar class' is a complete replacement for char and char * datatype. You can use 'mychar class' just like char and get much more functionalities. You should include the library 'libmychar.a' which you can build from the makefile given in Appendix H and copy the library to /usr/lib directory where all the "C++" libraries are located. To use the 'libmychar.a' compile your programs like -

        g++ example.cpp -lmychar

See illustration sample code as given below -

        mychar aa;

        aa = " Washington DC is the capital of USA ";

        // You can use aa.val like a 'char *' variable in programs !!
        for (unsigned long tmpii = 0; tmpii < aa.length(); tmpii++)
        {
                fprintf(stdout, "aa.val[%ld]=%c ", tmpii, aa.val[tmpii]);
        }

        // Using pointers on 'char *' val ...
        for (; *aa.val != 0; aa.val++)
        {
                fprintf(stdout, "aa.val=%c ", *aa.val);
        }

A complete example program "example_mychar.cpp" implementing the mychar class is given in Appendix A and mychar class is given in Appendix B.

3.1 Operators

The 'mychar class' provides these operators :-

Equal to ==
Not equal to !=
Assignment =
Add to itself and Assignment +=
String concatenation or addition +

For example to use operators -

        mychar aa;
        mychar bb("Bill Clinton");

        aa = "put some value string";  // assignment operator
        aa += "add some more"; // Add to itself and assign operator
        aa = "My name is" + " Alavoor Vasudevan "; // string cat operator

        if (bb == "Bill Clinton")  // boolean equal to operator
                cout << "bb is eqaul to 'Bill Clinton' " << endl;

        if (bb != "Al Gore")   // boolean 'not equal' to operator
                cout << "bb is not equal to 'Al Gore'" << endl;

3.2 Functions

The 'mychar class' provides these functions :-

Current string length length()
Left trim the string. Remove leading white-spaces - newlines, tabs ltrim()
Right trim the string. Remove trailing white-spaces - newlines, tabs rtrim()
Remove trailing and leading white-spaces trim()
Remove trailing newlines chop()
Change string to upper case to_upper()
Change string to lower case to_lower()
Truncate or round-off the float value roundf(float input_val, short precision)
Truncate or round-off the double value roundd(double input_val, short precision)
Find position, matching substr beginning from start pos(char *substr, unsigned long start)
Explodes the string and returns the list in the list-head pointer explodeH explode(char *seperator)
Implodes the strings in the list-head pointer explodeH and returns the mychar variable implode(char *glue)
Joins the strings in the list-head pointer explodeH and returns the mychar variable join(char *glue)
Repeat the input string n times repeat(char *input, unsigned int multiplier)
Reverse the string characters reverse()
Replace all occurences of string 'needle' with 'str' in the haystack 'val' replace(char *needle, char *str)
Translate certain chars str_tr(char *from, char *to)
Center the text string center(int length, char padchar = ' ')
Formats the original string by placing 'number' of 'padchar' characters between each set of blank-delimited words. Leading and Trailing blanks are always removed. If 'number' is omitted or is 0, then all spaces are in the string are removed. The default number is 0 and default padchar ' ' space(int number = 0, char padchar = ' ')
The result is string comprised of all characters between and including 'start' and 'end' xrange(char start, char end)
Removes any characters contained in 'list'. The default character for 'list' is a blank ' ' compress(char *list)
Deletes a portion of string of 'length' characters from 'start' position. If start is greater than the string length than string is unchanged delstr(int start, int length)
The 'newstr' in inserted into val beginning at 'start'. The 'newstr' will be padded or truncated to 'length' characters. The default 'length' is string length of newstr insert(char *newstr, int start = 0, int length = 0, char padchar = ' ')
The result is string of 'length' chars madeup of leftmost chars in val. Quick way to left justify a string left(int length = 0, char padchar = ' ')
The result is string of 'length' chars madeup of rightmost chars in val. Quick way to right justify a string right(int length = 0, char padchar = ' ')
The 'newstr' in overlayed into val beginning at 'start'. The 'newstr' will be padded or truncated to 'length' characters. The default 'length' is string length of newstr overlay(char *newstr, int start = 0, int length = 0, char padchar = ' ')
Sub-string, extract a portion of string substr(int start, int length = 0)
matches first match of regx at(char *regx)
Returns string before regx before(char *regx)
Returns string after regx after(char *regx)
Returns true if string is NULL value bool isnull()
Resets the string to NULL clear()

3.3 Miscellaneous Functions

Some miscellaneous mychar functions are given here, but DO NOT USE these, and instead use operators like '+', '+=', '==' etc.. These are 'private' members of the 'mychar' class.

Copy string str_cpy(char *bb)
Long integer converted to string str_cpy(unsigned long bb)
Integer converted to string str_cpy(int bb)
Float converted to string str_cpy(float bb)
String concatenate a char * str_cat(char *bb)
String concatenate a int str_cat(int bb)
String concatenate a int str_cat(unsigned long bb)
String concatenate a float str_cat(float bb)
Is equal to mychar ? bool equalto(const mychar & rhs, bool type = false)
Is equal to char* ? bool equalto(const char *rhs, bool type = false)

For example to convert integer to string do -

        mychar  aa;

        aa = 34;  // The '=' operator will convert int to string
        cout << "The value of aa is : " << aa.val << endl;

        aa = 234.878;  // The '=' operator will convert float to string
        cout << "The value of aa is : " << aa.val << endl;

        aa = 34 + 234.878;
        cout << "The value of aa is : " << aa.val << endl;
        // The output aa will be '268.878'

        // You must cast mychar to convert
        aa = (mychar) 34 + " Honourable President Ronald Reagan " + 234.878;
        cout << "The value of aa is : " << aa.val << endl;
        // The output aa will be '34 Honourable President Ronald Reagan 234.878'

4. C++ Zap (Delete) command

The delete and new commands in C++ are much better than the malloc and free functions of "C". Consider using new and zap (delete command) instead of malloc and free as much as possible.

To make delete command even more cleaner, make a Zap() command. Define a zap() command like this:

/* 
** Use do while to make it robust and bullet-proof macro.
** For example, if "do-while" is NOT used then results will be
** something else just as in -
** if (bbint == 4)
**              aa = 0
** else
**              zap(aptr);  // Problem!! aptr will be always set to NULL 
*/

#define zap(x) do { delete(x); x = NULL; } while (0)

The zap() command will delete the pointer and set it NULL. This will ensure that even if multiple zap()'s are called on the same deleted pointer then the program will not crash. For example -

        zap(pFirstname);
        zap(pFirstname); // no core dumps !! Because pFirstname is NULL now
        zap(pFirstname); // no core dumps !! Because pFirstname is NULL now

        zap(pLastname);
        zap(pJobDescription);

There is nothing magical about this, it just saves repetative code, saves typing time and makes programs more readable. The C++ programmers often forget to reset the deleted pointer to NULL, and this causes annoying problems causing core dumps and crashes. The zap() takes care of this automatically. Do not stick a typecast in the zap() command -- if something errors out on the above zap() command it likely has another error somewhere.

Also my_malloc() , my_realloc() and my_free() should be used instead of malloc(), realloc() and free(), as they are much cleaner and have additional checks. For an example, see the file "mychar.h" which is using the my_malloc() and my_free() functions.

5. Pointers are problems

A reference is an alias; when you create a reference, you initialize it with the name of another object, the target. From the moment on, the reference acts as an alternative name of the target, and anything you do to the reference is really done to the target.

Avoid using pointers as much as possible and use references. Pointers are really a great pain. It is possible to write a application without using pointers. In languages like Java, pointers are not supported at all !!

Syntax of References: Declare a reference by writing the type, followed by the reference operator (&), followed by the reference name. References MUST be initialized at the time of creation. For example -

        int             weight;
        int     & rweight = weight;

        DOG             aa;
        DOG & rDogRef = aa;

Do's of references -

Do use references to create an alias to an object
Do initialize all references
Do use references for high efficiency and performance of program.
Do use const to protect references and pointers whenever possible.

Do not's of references -

IMPORTANT: Don't use references to NULL objects !!!!
Don't confuse the address of operator & with reference operator !! The references are used in the declarations section (see Syntax of References above).
Don't try to reassign a reference
Don't use pointers if references will work
Don't return a reference to a local object
Don't pass by reference if the item referred to may go out of scope

6. Usage of my_malloc and my_free

Try to avoid using malloc and realloc as much as possible and use new and zap(delete). But sometimes you may need to use the "C" style memory allocations in "C++". Use the functions my_malloc() , my_realloc() and my_free(). These functions do proper allocations and initialisations and try to prevent memory problems. Also these functions (in DEBUG mode) can keep track of memory allocated and print total memory usage before and after the program is run. This tells you if there are any memory leaks.

The my_malloc and my_realloc is defined as below. It allocates little more memory (SAFE_MEM = 5) and initializes the space and if it cannot allocate it exits the program. The 'call_check(), remove_ptr()' functions are active only when DEBUG is defined in makefile and are assigned to ((void)0) i.e. NULL for non-debug production release. They enable the total-memory used tracing.

void *local_my_malloc(size_t size, char fname[], int lineno) 
{
        size_t  tmpii = size + SAFE_MEM;
        void *aa = NULL;
        aa = (void *) malloc(tmpii);
        if (aa == NULL)
                raise_error_exit(MALLOC, VOID_TYPE, fname, lineno);
        memset(aa, 0, tmpii);
        call_check(aa, tmpii, fname, lineno);
        return aa;
}

char *local_my_realloc(char *aa, size_t size, char fname[], int lineno)
{
        remove_ptr(aa, fname, lineno);
        unsigned long tmpjj = 0;
        if (aa) // aa !=  NULL
                tmpjj = strlen(aa);
        unsigned long tmpqq = size + SAFE_MEM;
        size_t  tmpii = sizeof (char) * (tmpqq);
        aa = (char *) realloc(aa, tmpii);
        if (aa == NULL)
                raise_error_exit(REALLOC, CHAR_TYPE, fname, lineno);

        // do not memset!! memset(aa, 0, tmpii);
        aa[tmpqq-1] = 0;
        unsigned long kk = tmpjj;
        if (tmpjj > tmpqq)
                kk = tmpqq;
        for ( ; kk < tmpqq; kk++)
                aa[kk] = 0;
        call_check(aa, tmpii, fname, lineno);
        return aa;
}

See my_malloc.cpp. and the header file my_malloc.h. for full implementation of the my_malloc program.

An example on usage of my_malloc and my_free as below:

        char    *aa;
        int     *bb;
        float   *cc;
        aa = (char *) my_malloc(sizeof(char)* 214);
        bb = (int *) my_malloc(sizeof(int) * 10);
        cc = (float *) my_malloc(sizeof(int) * 20);

        aa = my_realloc(aa, sizeof(char) * 34);
        bb = my_realloc(bb, sizeof(int) * 14);
        cc = my_realloc(cc, sizeof(float) * 10);

Note that in my_realloc you do not need to cast the datatype as the variable itself is passed and correct my_realloc is called which returns the proper datatype pointer. The my_realloc has overloaded functions for char*, int* and float*.

7. Debug files

To debug any C++ or C programs include the file debug.h and in your 'Makefile' define DEBUG to turn on the traces from the debug.h functions. When you remove the '-DDEBUG' then the debug function calls are set to ((void)0) i.e. NULL, hence it has no impact on final production release version of project. You can generously use the debug functions in your programs and it will not increase the size of production executable.

See the file debug.cpp for implementation of debug routines. And see the file my_malloc.cpp for sample which uses debug.h and debug functions.

See the sample Makefile .

8. C++ Online-Docs

Visit the following C++ sites :-

C++ Crash-proof site http://www.troubleshooters.com/codecorn/crashprf.htm
C++ Memory site http://www.troubleshooters.com/codecorn/memleak.htm

Internet has vast amounts of documentation on C++. Visit the search engines like Yahoo, Lycos, Infoseek, Excite. Type in the keywords 'C++ tutorials' 'C++ references' 'C++ books' . You can narrow down the search criteria by clicking on Advanced search and select search by exact phrase

8.1 C++ Tutorials

There are many on-line tutorials available on internet. Type 'C++ tutorials' in the search engine.

8.2 C++ Coding Standards

Visit the C++ Coding Standards URLs

C++ coding standard http://www.cs.umd.edu/users/cml/cstyle/CppCodingStandard.html
Coding standards from Possibility http://www.possibility.com/Cpp/CppCodingStandard.html
Coding standards from Ambysoft http://www.ambysoft.com/javaCodingStandards.html
Rules and recommendations http://www.cs.umd.edu/users/cml/cstyle/
Indent and annotate http://www.cs.umd.edu/users/cml/cstyle/indhill-annot.html
Elemental rules http://www.cs.umd.edu/users/cml/cstyle/Ellemtel-rules.html
C++ style doc http://www.cs.umd.edu/users/cml/cstyle/Wildfire-C++Style.html

8.3 C++ Quick-Reference

Type 'C++ Reference' in the search engine.

8.4 C++ Usenet Newsgroups

C++ newsgroups : comp.lang.c++.announce
C++ newsgroups : comp.lang.c++.*

9. Memory Tools

Use the following memory debugging tools

On linux contrib cdrom see mem_test*.rpm package
On linux cdrom see ElectricFence*.rpm package
Purify Tool from Rational Software Corp http://www.rational.com
Insure++ Tool from Parasoft Corp http://www.parasoft.com
Linux Tools at http://www.xnet.com/~blatura/linapp6.html#tools
Search the Internet engines like Yahoo, Lycos, Excite, Mamma.com for keyword "Linux memory debugging tools".

10. Related URLs

Visit following locators which are related to C, C++ -

Vim color text editor for C++, C http://metalab.unc.edu/LDP/HOWTO/Vim-HOWTO.html
C++ Beautifier HOWTO http://metalab.unc.edu/LDP/HOWTO/C-C++Beautifier-HOWTO.html
CVS HOWTO for C++ programs http://metalab.unc.edu/LDP/HOWTO/CVS-HOWTO.html
Linux goodies main site http://www.aldev.8m.com
Linux goodies mirror site http://aldev.webjump.com

11. Other Formats of this Document

This document is published in 11 different formats namely - DVI, Postscript, Latex, Adobe Acrobat PDF, LyX, GNU-info, HTML, RTF(Rich Text Format), Plain-text, Unix man pages and SGML.

You can get this HOWTO document as a single file tar ball in HTML, DVI, Postscript or SGML formats from - ftp://metalab.unc.edu/pub/Linux/docs/HOWTO/other-formats/ or ftp://metalab.unc.edu/pub/Linux/docs/HOWTO/other-formats/
Plain text format is in: ftp://metalab.unc.edu/pub/Linux/docs/HOWTO or ftp://metalab.unc.edu/pub/Linux/docs/HOWTO
Translations to other languages like French, German, Spanish, Chinese, Japanese are in ftp://metalab.unc.edu/pub/Linux/docs/HOWTO or ftp://metalab.unc.edu/pub/Linux/docs/HOWTO Any help from you to translate to other languages is welcome.

The document is written using a tool called "SGML tool" which can be got from - http://www.xs4all.nl/~cg/sgmltools/ Compiling the source you will get the following commands like

sgml2html C++Programming-HOWTO.sgml (to generate html file)
sgml2rtf C++Programming-HOWTO.sgml (to generate RTF file)
sgml2latex C++Programming-HOWTO.sgml (to generate latex file)

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Also you can find this document at the following mirrors sites -

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Other mirror sites near you (network-address-wise) can be found at http://metalab.unc.edu/LDP/hmirrors.html select a site and go to directory /LDP/HOWTO/C++Programming-HOWTO.html

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        To read dvi document give the command -
                xdvi -geometry 80x90 howto.dvi
        And resize the window with mouse. See man page on xdvi. 
        To navigate use Arrow keys, Page Up, Page Down keys, also
        you can use 'f', 'd', 'u', 'c', 'l', 'r', 'p', 'n' letter
        keys to move up, down, center, next page, previous page etc.
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You can read postscript file using the program 'gv' (ghostview) or 'ghostscript'. The ghostscript program is in ghostscript*.rpm package and gv program is in gv*.rpm package in Redhat Linux which can be located through ControlPanel | Applications | Graphics menu buttons. The gv program is much more user friendly than ghostscript. Ghostscript and gv are also available on other platforms like OS/2, Windows 95 and NT.

Get ghostscript for Windows 95, OS/2, and for all OSes from http://www.cs.wisc.edu/~ghost


        To read postscript document give the command -
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                ghostscript howto.ps

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12. Copyright

Copyright policy is GNU/GPL as per LDP (Linux Documentation project). LDP is a GNU/GPL project. Additional requests are - you must retain the author's name, email address and this copyright notice on all the copies. If you make any changes or additions to this document then you please intimate all the authors of this document.