What's the Difference Between Cstdlib and Stdlib.H

What's the difference between cstdlib and stdlib.h?

The first one is a C++ header and the second is a C header. Since the first uses a namespace, that would seem to be preferable.

What's the main difference between stdlib.h and cstdlib in C++?

As EXIT_FAILURE is a macro, it makes no difference which you include. The cstdlib version will put the names of all the functions into the std namespace, so you can say things like:

std::exit(0);

but as macros don't respect namespaces, you can't say:

std::EXIT_FAILURE

difference between header files “stdio.h” and “stdlib.h”

One has set of function declarations, constants, macros and type definitions, the other has a different set of function declarations, constants, macros and type definitions. You are able to open the file with a simple text editor if you want to see the contents.

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stdio stands for standard input/output, its contents are usually but not exclusively related to input output operations, either with hardware or physical devices or with files supported by the system. A list of functions declarations, macros and type definitions available can be found here:

Functions:

• Operations on files:

  • remove - Remove file

  • rename - Rename file

  • tmpfile - Open a temporary file

  • tmpnam - Generate temporary filename

• File access:

  • fclose - Close file

  • fflush - Flush stream

  • fopen - Open file

  • freopen - Reopen stream with different file or mode

  • setbuf - Set stream buffer

  • setvbuf - Change stream buffering

• Formatted input/output:

  • fprintf - Write formatted data to stream

  • fscanf - Read formatted data from stream

  • printf - Print formatted data to stdout

  • scanf - Read formatted data from stdin

  • snprintf - Write formatted output to sized buffer

  • sprintf - Write formatted data to string

  • sscanf - Read formatted data from string

  • vfprintf - Write formatted data from variable argument list to stream

  • vfscanf - Read formatted data from stream into variable argument list

  • vprintf - Print formatted data from variable argument list to stdout

  • vscanf - Read formatted data into variable argument list

  • vsnprintf - Write formatted data from variable argument list to sized buffer

  • vsprintf - Write formatted data from variable argument list to string

  • vsscanf - Read formatted data from string into variable argument list

• Character input/output:

  • fgetc - Get character from stream

  • fgets - Get string from stream

  • fputc - Write character to stream

  • fputs - Write string to stream

  • getc - Get character from stream

  • getchar - Get character from stdin

  • gets - Get string from stdin

  • putc - Write character to stream

  • putchar - Write character to stdout

  • puts - Write string to stdout

  • ungetc - Unget character from stream

• Direct input/output:

  • fread - Read block of data from stream

  • fwrite - Write block of data to stream

• File positioning:

  • fgetpos - Get current position in stream

  • fseek - Reposition stream position indicator

  • fsetpos - Set position indicator of stream

  • ftell - Get current position in stream

  • rewind - Set position of stream to the beginning

• Error-handling:

  • clearerr - Clear error indicators

  • feof - Check end-of-file indicator

  • ferror - Check error indicator

  • perror - Print error message

Macros:

• BUFSIZ - Buffer size

• EOF - End-of-File

• FILENAME_MAX - Maximum length of file names

• FOPEN_MAX - Potential limit of simultaneous open streams

• L_tmpnam - Minimum length for temporary file name

• NULL - Null pointer (macro )

• TMP_MAX - Number of temporary files

• Additionally: _IOFBF, _IOLBF, _IONBF (used with setvbuf)
  and SEEK_CUR, SEEK_END and SEEK_SET (used with fseek).

Types:

• FILE - Object containing information to control a stream

• fpos_t - Object containing information to specify a position within a file

• size_t - Unsigned integral type

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stdlib stands for standard library and it has general purpose functions, including dynamic memory management, random number generation, communication, arithmetics, searching, sorting and converting, etc. A list of functions declarations, macros and type definitions available can be found here:

Functions

• String conversion

  • atof - Convert string to double

  • atoi - Convert string to integer

  • atol - Convert string to long integer

  • atoll - Convert string to long long integer

  • strtod - Convert string to double

  • strtof - Convert string to float

  • strtol - Convert string to long integer

  • strtold - Convert string to long double

  • strtoll - Convert string to long long integer

  • strtoul - Convert string to unsigned long integer

  • strtoull - Convert string to unsigned long long integer

• Pseudo-random sequence generation

  • rand - Generate random number

  • srand - Initialize random number generator

• Dynamic memory management

  • calloc - Allocate and zero-initialize array

  • free - Deallocate memory block

  • malloc - Allocate memory block

  • realloc - Reallocate memory block

• Environment

  • abort - Abort current process

  • atexit - Set function to be executed on exit

  • at_quick_exit - Set function to be executed on quick exit

  • exit - Terminate calling process

  • getenv - Get environment string

  • quick_exit - Terminate calling process quick

  • system - Execute system command

  • _Exit - Terminate calling process

• Searching and sorting

  • bsearch - Binary search in array

  • qsort - Sort elements of array

• Integer arithmetics

  • abs - Absolute value

  • div - Integral division

  • labs - Absolute value

  • ldiv - Integral division

  • llabs - Absolute value

  • lldiv - Integral division

• Multibyte characters

  • mblen - Get length of multibyte character

  • mbtowc - Convert multibyte sequence to wide character

  • wctomb - Convert wide character to multibyte sequence

• Multibyte strings

  • mbstowcs - Convert multibyte string to wide-character string

  • wcstombs - Convert wide-character string to multibyte string

Macro constants

• EXIT_FAILURE - Failure termination code

• EXIT_SUCCESS - Success termination code

• MB_CUR_MAX - Maximum size of multibyte characters

• NULL - Null pointer

• RAND_MAX - Maximum value returned by rand

Types

• div_t - Structure returned by div

• ldiv_t - Structure returned by ldiv

• lldiv_t - Structure returned by lldiv

• size_t - Unsigned integral type

Updating legacy C code headers to C++ stdlib

Your code may change in very subtle ways, due to the fact that the C++ standard headers use overloading where C used different names. This is most likely to cause trouble with cmath.

stdlib.h isn't going anywhere, so feel free to keep using it.

For example, compare:

#include <iostream>
using namespace std;

#include <stdlib.h>
#include <math.h>

int main(void)
{
    double x = -2;
    cout << (3/abs(x)) << endl;
    return 0;
}

The results before and after switching to C++ headers are very different, even though the exact same C++ compiler and options are used in both cases.

When using C headers in C++, should we use functions from std:: or the global namespace?

From the C++11 Standard (emphasis mine):

D.5 C standard library headers [depr.c.headers]

1. For compatibility with the C standard library ...
2. Every C header, each of which has a name of the form name.h, behaves as if each name placed in the standard
   library namespace by the corresponding cname header is placed within the global namespace scope. It is unspecified whether these names are first declared or defined within namespace scope (3.3.6) of the namespace std and are then injected into the global namespace scope by explicit using-declarations (7.3.3).
3. Example: The header <cstdlib> assuredly provides its declarations and definitions within the namespace
   std. It may also provide these names within the global namespace. The header <stdlib.h> assuredly provides the same declarations and definitions within the global namespace, much as in the C Standard. It
   may also provide these names within the namespace std.

Using the «name.h» headers is deprecated, they have been identified as candidates for removal from future revisions.

So, I would suggest to include the «cname» headers and to use the declarations and definitions from the std namespace.

If you have to use the «name.h» headers for some reasons (it's deprecated, see above), I would suggest to use the declarations and definitions from the global namespace.

In other words: prefer

#include <cstdio>

int main() {
    std::printf("Hello world\n");
}

over

#include <stdio.h>

int main() {
    printf("Hello world\n");
}

Generating the partitions of a number

It's called Partitions. [Also see Wikipedia: Partition (number theory).]

The number of partitions p(n) grows exponentially, so anything you do to generate all partitions will necessarily have to take exponential time.

That said, you can do better than what your code does. See this, or its updated version in Python Algorithms and Data Structures by David Eppstein.

Read files with stdlib.h C++

FILE is an opaque type; the C standard doesn't define its fields, so they can vary between implementations. Your program expects the FILE type to have fields with certain names, but your system doesn't actually define it that way.

Don't rely on FILE having specific fields, and don't dereference a FILE* to try to access those fields. Instead, use the functions provided by the C standard library, such as fread to read contents and ftell to get the current position. These functions take a FILE* parameter and access its contents in whatever way is correct for the system where the program is running.

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