最近做cache lab 用到了getopt函數(shù), 用man 3 getopt查看了下用法, 做個總結(jié).

描述：getopt函數(shù)是用來解析命令行參數(shù)的, 以‘-’或‘--’開頭的參數(shù)為選項元素，除去‘-’或‘--’的選項元素

為選項字符。如果getopt函數(shù)被重復(fù)調(diào)用，則它將會依次返回每個選項元素中的選項字符。

使用getopt函數(shù)需要包含以下頭文件:

#include

#include

有幾個全局變量與getopt函數(shù)解析參數(shù)有關(guān):

optind: int型, 指示下一個要解析的參數(shù)位置，初始時為1.

optarg: char *, 必須接參數(shù)的選項元素的參數(shù), 如上面的-nxzz, optarg 就指向"xzz"字符串.

opterr: int 型, 設(shè)為0將不打印錯誤信息.

函數(shù)原型為: int getopt(int argc, char * const argv[], const char *optstring);

參數(shù)說明: 前兩個參數(shù)與main函數(shù)參數(shù)相同, argc保存參數(shù)個數(shù)，argv[]保存參數(shù)數(shù)組，第三個參數(shù)optstring是你定義

的選項字符組成的字符串, 如"abc",表示該命令有三個選項元素 -a, -b, -c, 選項字符后面如果有一個冒號說

明該選項元素一定有一個參數(shù), 且該參數(shù)保存在optarg中, 如"n:t",

表示選項元素n后要接參數(shù), 選項元素t后

不接參數(shù)，如 -n xzz -t 或 -nxzz t,有兩個冒號說明該選項可接可選參數(shù), 但可選參數(shù)不保存在optarg中.

返回值: 如果當前處理的參數(shù)為選項元素，且該選項字符在optstring字符串中, 即為你定義的選項, 則返回該

選項字符，如果該選項字符不是你定義的, 那么返回字符'?', 并更新全局變量optind, 指向argc數(shù)組中的下一

個參數(shù). 如果當前處理的參數(shù)不是選項元素, 則optind偏移向下一個參數(shù), 直到找到第一個選項元素為止, 然后

再按之前描述的操作,如果找不到選項元素, 說明解析結(jié)束, 則返回-1.

下面看例子:

#include

#include

int main(int argc, char * const argv[])

{

int opt;

while ((opt = getopt(argc, argv, "nb:o::t")) != -1) {

printf("opt = %c, optarg = %s, optind = %d, argv[%d] = %sn",

opt, optarg, optind, optind, argv[optind]);

}

return 0;

}

假設(shè)編譯好的可執(zhí)行文件名為test, test有3個有效參數(shù)-n, -b, -t, 其中-n, -t后不接參數(shù), -b后一定要接參數(shù), -o后接可選參數(shù).

# ./test -x -y -z <------ 無效參數(shù), 會打印錯誤信息, 并返回字符'?'

輸出:

./getopt: invalid option -- 'x'

opt = ?, optarg = (null), optind = 2, argv[2] = -y

./getopt: invalid option -- 'y'

opt = ?, optarg = (null), optind = 3, argv[3] = -z

./getopt: invalid option -- 'z'

opt = ?, optarg = (null), optind = 4, argv[4] = (null)

# ./test -n -b xzz -t

opt = n, optarg = (null), optind = 2, argv[2] = -b

opt = b, optarg = xzz, optind = 4, argv[4] = -t <----------- optarg 指向選項元素的參數(shù), 并且optind跳過了該參數(shù), 直接指向了-t參數(shù)

opt = t, optarg = (null), optind = 5, argv[5] = (null)

# ./test -n -bxzz -t <------------- 也可將選項參數(shù)與其接的參數(shù)寫在一起

opt = n, optarg = (null), optind = 2, argv[2] = -bxzz

opt = b, optarg = xzz, optind = 3, argv[3] = -t <----------- optind 同樣將指向下一個參數(shù)-t

opt = t, optarg = (null), optind = 4, argv[4] = (null)

# ./test -b -t

opt = b, optarg = -t, optind = 3, argv[3] = (null) <----------- 將-t當成了選項元素-b的參數(shù), 之后就不再解析-t, optind為3

# ./test -t -b <---- -b缺少參數(shù)

opt = t, optarg = (null), optind = 2, argv[2] = -b

./getopt: option requires an argument -- 'b'

opt = ?, optarg = (null), optind = 3, argv[3] = (null)

# ./test -t a -b xzz <------- 命令行中有一個無用參數(shù) a, 解析時被忽略了, 因為-t不需要接參數(shù)

opt = t, optarg = (null), optind = 2, argv[2] = a

opt = b, optarg = xzz, optind = 5, argv[5] = (null)

# ./test -ntb xzz <--------- 還可以把參數(shù)連在一起寫

opt = n, optarg = (null), optind = 1, argv[1] = -ntb

opt = t, optarg = (null), optind = 1, argv[1] = -ntb

opt = b, optarg = xzz, optind = 3, argv[3] = (null)

# ./test -t -o -b xzz <----- -o選項不接參數(shù)

opt = t, optarg = (null), optind = 2, argv[2] = -o

opt = o, optarg = (null), optind = 3, argv[3] = -b

opt = b, optarg = xzz, optind = 5, argv[5] = (null)

# ./test -t -o 10 -b xzz <------ -o選項接參數(shù)10

opt = t, optarg = (null), optind = 2, argv[2] = -o

opt = o, optarg = (null), optind = 3, argv[3] = 10 <------------------ 可以看到10并沒有保存在optarg中

opt = b, optarg = xzz, optind = 6, argv[6] = (null) <----------------- 而-b的參數(shù)則保存在optarg中了

常用用法:

一般是用while循環(huán)配合switch語句來使用getopt函數(shù)解析參數(shù), 如下:

/*

* 得到參數(shù)信息

*/

int getinfo(int argc, char * const argv[], int *ps, int *pE, int *pb, char *trace_name, int *vflag)

{

int opt;

int count_arg = 0;

opterr = 0;

while ((opt = getopt(argc, argv, "vs:E:b:t:")) != -1) {

switch (opt) {

case 'v':

*vflag = 1;

break;

case 's':

++count_arg;

*ps = atoi(optarg);

break;

case 'E':

++count_arg;

*pE = atoi(optarg);

break;

case 'b':

++count_arg;

*pb = atoi(optarg);

break;

case 't':

++count_arg;

strcpy(trace_name, optarg);

break;

default: /* '?' */

Usage();

exit(-1);

break;

}

}

if (count_arg < 4) {

Usage();

exit(-1);

}

return 0;

}