LINUX Study Notes 14 -- inter-process communication 3 shared memory

A) meaning: multiple processes share part of the physical memory. Fast access, convenient B) first create shared memory: intshmget (key_tkey, intsize, intshmflg) 1.Key: indicates the shared memory key value; 0/IPC_PRIVATEa) Key0: this is not created, however, if the shmflg is still... a) meaning: multiple processes share part of the physical memory. Fast and convenient access
 
B) create shared memory first: int shmget (key_t key, int size, int shmflg)
 
1. Key: indicates the Key value of shared memory; 0/IPC_PRIVATE
 
A) Key = 0: this is not created, but it is still created if shmflg is still IPC_PRIVATE.
 
2. Size: Size
 
3. Shmflg: Mark S_IRUSR | S_IWUSR
 
4. return value: the shared memory identifier is returned successfully;-1 is returned if a failure occurs;
 
5. # include , # Include , # Include , # Include
 
C) re-map the shared memory:
 
1. Int shmat (int shmid, char * shmaddr, int flag)
 
A) Shmid: shared storage identifier returned by the shmget function
 
B) Shmaddr: used to save the ing address. if it is set to 0, the system automatically finds the address and returns the value.
 
C) Flag: used to determine the ing address (usually 0)
 
D) return value: if shmaddr is set to 0, the shared memory is successfully mapped to the address in the process. if shmaddr is set to 0,-1 is returned.
 
2. the shared memory is mapped to different processes with different addresses.
 
D) clear content: after obtaining the address, you need to reset the data in this memory zone first.
 
1. memset (p_addr, '\ 0', 1024): reset all 1024 bytes
 
A) # include
 
E) copy content: strncpy (p_addr, argv [1], 1024)
 
F) un ing: int shmdt (char * shmaddr)