C Reference function atexit()

With the function atexit() it is possible to set a function that will be executed on termination of the program.

Usage of atexit():

int atexit ( void ( * func ) (void) );

If the program is terminated normally then the function pointed by the func pointer argument is called.
If there are more then one atexit functions (multiple calls) then they are all executed in reverse order as the where stacked. More »


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C Reference function abort()

This function of stdlib will abort the current process.

Usage of abort():

void abort ( void );

The function aborts the process with an abnormal program termination.
The function abort will generate a signal SIGABRT. This signal will by default causes the program to terminate.

Parameters:

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C Reference function system()

The function system() will invoke the command processor to execute a command. If the command execution is terminated the processor will give the control back to the program that has called the system command.

Usage of system():

int system ( const char * command );

It will return an integer value, which is interpretation is different on various systems, thus system dependent.
If you want to check whether there is a command processor exist then you use the NULL argument in the function. More »


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C Reference function calloc()

The function calloc() will allocate a block of memory for an array. All of these elements are size bytes long. During the initialization all bits are set to zero.

Usage of calloc():

void * calloc ( size_t num, size_t size );

Parameters:

Number of elements (array) to allocate and the size of elements.

Return value:

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C Reference function realloc()

The function realloc() reallocates a memory block with a specific new size. If you call realloc() the size of the memory block pointed to by the pointer is changed to the given size in bytes. This way you are able to expand and reduce the amount of memory you want to use (if available of course.)

It is possible that the function moves the memory block to a new location, in which way the function will return this new location. If the size of the requested block is larger then the previous block then the value of the new portion is indeterminate.

If the pointer is NULL then the function will behave exactly like the function malloc(). It will assign a new block of a size in bytes and will return a pointer to it.

If the size is 0 then the memory that was previously allocated is freed as if a call of the function free() was given. It will return a NULL pointer in that case. More »


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C Reference function malloc()

The function malloc() will allocate a block of memory that is size bytes large. If the requested memory can be allocated a pointer is returned to the beginning of the memory block.

Note: the content of the received block of memory is not initialized.

Usage of malloc():

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C Reference function free()

If you have allocated a memory block with the functions malloc(), calloc() or realloc() then you need to free the previously allocated memory.

Usage of free():

void free ( void * ptr );

Parameters:

The parameter is a pointer to a memory block that was allocated with malloc(), calloc() or realloc(). If you pass a null pointer then there will no action occur. More »


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C Reference function srand() initialize random number generator

This function of stdlib will initialize the random number generator that can be used with the rand() function.

Usage of srand():

void srand ( unsigned int seed );

The function srand() is used to initialize the pseudo-random number generator by passing the argument seed.
Often the function time is used as input for the seed. More »


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C Reference function rand() generate a random number

This function of stdlib will generate a random number.

Usage of rand():

int rand (void);

Parameters:

The function rand() returns a pseudo-random integral number.
This number will be in the range 0 to RAND_MAX. The algorithm of rand() uses a seed to generate the series of numbers, this is why srand must be used to initialize the seed to some distinctive value.

The constant RAND_MAX is defined in standard library (stdlib). More »


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C Reference function strtol()

This function of stdlib will convert a string to long integer.

Usage of strtol():

long int strtol ( const char * str, char ** endptr, int base );

Parameters:

C string str interpreting its content as an integral number of the specified base, which is returned as a long int value. If endptr is not a null pointer, the function also sets the value pointed by endptr to point to the first character after the number. White-spaces are discarded until the first non-whitespace character is found. More »


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