The function getenv() of the stdlib.h will get the environment string.
char * getenv ( const char * name );
The function will retrieve a C string that is containing a value of the environment variable, which is specified with the name argument.
The name of the variable that you want to get.
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The function exit() will terminate the process that calls the exit.
void exit ( int status );
On call the process will terminate normally. It will perform regular cleanup as normal for a normal ending process. (For example atexit functions are executed.)
A status value returned to the parent process.
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With the function atexit() it is possible to set a function that will be executed on termination of the program.
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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This function of stdlib will abort the current process.
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.
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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.
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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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.
void * calloc ( size_t num, size_t size );
Number of elements (array) to allocate and the size of elements.
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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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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.
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If you have allocated a memory block with the functions malloc(), calloc() or realloc() then you need to free the previously allocated memory.
void free ( void * ptr );
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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This function of stdlib will initialize the random number generator that can be used with the rand() function.
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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