E.10. Dynamic Memory Allocation with calloc and realloc

In Chapter 10, we discussed C++-style dynamic memory allocation with new and delete. C++ programmers should use new and delete, rather than C's functions malloc and free (header ). However, most C++ programmers will find themselves reading a great deal of C legacy code, and therefore we include this additional discussion on C-style dynamic memory allocation.

The general utilities library () provides two other functions for dynamic memory allocationcalloc and realloc. These functions can be used to create and modify dynamic arrays. As shown in Chapter 8, Pointers and Pointer-Based Strings, a pointer to an array can be subscripted like an array. Thus, a pointer to a contiguous portion of memory created by calloc can be manipulated as an array. Function calloc dynamically allocates memory for an array and initializes the memory to zeroes. The prototype for calloc is

 void *calloc( size_t nmemb, size_t size );

It receives two argumentsthe number of elements (nmemb) and the size of each element (size)and initializes the elements of the array to zero. The function returns a pointer to the allocated memory or a null pointer (0) if the memory is not allocated.

Function realloc changes the size of an object allocated by a previous call to malloc, calloc or realloc. The original object's contents are not modified, provided that the memory allocated is larger than the amount allocated previously. Otherwise, the contents are unchanged up to the size of the new object. The prototype for realloc is


 void *realloc( void *ptr, size_t size );

Function realloc takes two argumentsa pointer to the original object (ptr) and the new size of the object (size). If ptr is 0, realloc works identically to malloc. If size is 0 and ptr is not 0, the memory for the object is freed. Otherwise, if ptr is not 0 and size is greater than zero, realloc TRies to allocate a new block of memory. If the new space cannot be allocated, the object pointed to by ptr is unchanged. Function realloc returns either a pointer to the reallocated memory or a null pointer.

Common Programming Error E.2

Using the delete operator on a pointer resulting from malloc, calloc and realloc. Using realloc or free on a pointer resulting from the new operator.


Introduction to Computers, the Internet and World Wide Web

Introduction to C++ Programming

Introduction to Classes and Objects

Control Statements: Part 1

Control Statements: Part 2

Functions and an Introduction to Recursion

Arrays and Vectors

Pointers and Pointer-Based Strings

Classes: A Deeper Look, Part 1

Classes: A Deeper Look, Part 2

Operator Overloading; String and Array Objects

Object-Oriented Programming: Inheritance

Object-Oriented Programming: Polymorphism

Templates

Stream Input/Output

Exception Handling

File Processing

Class string and String Stream Processing

Web Programming

Searching and Sorting

Data Structures

Bits, Characters, C-Strings and structs

Standard Template Library (STL)

Other Topics

Appendix A. Operator Precedence and Associativity Chart

Appendix B. ASCII Character Set

Appendix C. Fundamental Types

Appendix D. Number Systems

Appendix E. C Legacy Code Topics

Appendix F. Preprocessor

Appendix G. ATM Case Study Code

Appendix H. UML 2: Additional Diagram Types

Appendix I. C++ Internet and Web Resources

Appendix J. Introduction to XHTML

Appendix K. XHTML Special Characters

Appendix L. Using the Visual Studio .NET Debugger

Appendix M. Using the GNU C++ Debugger

Bibliography

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C++ How to Program
C++ How to Program (5th Edition)
ISBN: 0131857576
EAN: 2147483647
Year: 2004
Pages: 627
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