C語言 - 轉型態

[例1, Convert string to long integer, argv[0]為string型態]

[prototype]
long int atol ( const char * str );


[sample code]
#include
#include

   int ch_num =0;
   ch_num = atol (argv[0]);

/*此例子會把argv[0]的型態從string轉成int存放到ch_num去 [1]
 *see Reference[1]
 */

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[例2, 把IP位址從string型態轉成二進位的數字, argv[0]為string型態]

[prototype]
int inet_aton(const char * cp,struct in_addr *inp);


[sample code]
#include
#include
#include

int ch_num =0;
inet_aton(argv[0], &ch_num);  //存放變數記得用pointer

/*
 *此例子會把argv[0]的string型態從網路位址(ex.140.115.152.231)
 *轉成二進制的數字
 *延伸閱讀：inet_addr，inet_ntoa
 *see Reference[2]
*/

-----------------------------------------------
[例3. convert address from presentation format to network format ]

[sample code]
#include "inet.h"

int ip=0;

inet_pton(AF_INET, argv[0], &ip);

/*
* 把argv[0]的string型態轉成ipv4的位址型態
* see reference[4]
*/


-----------------------------------------------

[例4. 把int 轉成 string]  /* Convert integer to string (non-standard function) */

char * itoa ( int value, char * str, int base );


另一種用法為sprintf: [5]
ex.

• sprintf(str,"%d",value) converts to decimal base.
• sprintf(str,"%x",value) converts to hexadecimal base.
• sprintf(str,"%o",value) converts to octal base.

-----------------------------------------------
[例5. 把type ip4a 轉成char[ ] ]  /* non-standard function) */

inet_ntoar(ip4a IP, char*[] )

ex.
ip4a IP;
char ip_str[INETADDR_LEN];

inet_ntoar(IP, ip_str);




References：
[1]http://www.cplusplus.com/reference/clibrary/cstdlib/atol/
[2]http://www.cs.nctu.edu.tw/~yslin/library/linuxc/function/14.html
[3]http://www.csie.ntnu.edu.tw/~u91029/libtech.html
[4]http://www.mkssoftware.com/docs/man3/inet_pton.3.asp
[5]http://www.cplusplus.com/reference/clibrary/cstdlib/itoa/