Linux parsing command line options getopt

Linux parsing command line options Getopt_long usage

In the process of inevitable need to use command-line options, you can choose to parse the command-line options, but there are ready-made, why rebuild the wheel.

The following is a description of using Getopt_long to resolve command-line options.

The main use of the program:

Whether the short option long option requires parameter comments

-V--version no query version number

-N--name is (user name) specifies the consumer

-D--debug Whether it has been tested

1. Function source

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The code is as follows:

[CPP]

#include //getopt_long () header file location

int Getopt_long (int ___argc, char *const *___argv,

const Char *__shortopts,

const struct Option *__longopts, int *__longind);

int getopt_long_only (int ___argc, char *const *___argv,

const Char *__shortopts,

const struct Option *__longopts, int *__longind);

2. Parameter Introduction

ARGC argv: Passed directly from main function

Shortopts: Short option string. As "n:v", it should be pointed out that the short option string does not need '-', but the option needs to pass the parameter, after the short option followed by ":".

Longopts:struct option Array, for holding long option arguments.

Longind: Used to return the index value of a long option in an array of longopts structures for debugging. Normal to NULL

Below is a description of struct option

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The code is as follows:

[CPP]

struct option

{

const char *name;//long option name

int has_arg;//Whether parameters are required

int *flag;

int Val;

};

Name: Long option names

Has_arg: Parameters are required. The value has three different cases

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The code is as follows:

[CPP]

# define No_argument 0//No parameters required

# define Required_argument 1//must specify parameters

# define Optional_argument 2//parameter optional

Flag and Val

Flag and Val are interdependent, mainly in two ways:

(1), flag is the Null,val value used to determine the long option, so you need to specify a unique Val value for the long option. A bridge is also built for long options and short options.

(2), flag is not NULL, the Val value is stored in the storage space that the flag points to, identifying the long option that appears.

3, return value

Use short options in your program to return a short option character (such as ' n '), and then save the argument to Optarg before returning it when the parameter is required.

The long option is used in the program, and the return value is determined by flag and Val. Returns the Val value when flag is null. So different processing is done according to the Val value, which also shows that Val must be unique. When the Val value is equal to the short option value, the short option resolves the function resolution long option, and when flag is not NULL, the Val value is saved to the storage point flag, Getopt_long returns 0

There are undefined long options or short options, Getopt_long returns?

Parsing completed, Getopt_long return-1

4. Example

Theory should be combined with reality

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The code is as follows:

[CPP]

#include

#include

#include //getopt_long () header file location

int main (int argc, char** argv)

{

const char *optstring= "N:V";

int c,deb,index;

struct option opts[]={{"username", Required_argument,null, ' n '},

{"Version", No_argument,null, ' V '},

{"Debug", no_argument,&deb,1},

{0,0,0,0}};

while ((C=getopt_long (Argc,argv,optstring,opts,&index))!=-1)

{

Switch (c)

{

Case ' n '://-n or--username Specify user name

printf ("username is%sn", optarg);

Break

Case ' V '://-v or--version, output version number

printf ("version is 0.0.1 n");

Break

Case 0://flag NOT NULL

printf ("Debug is%dn", Deb);

Break

Case '? ':/ /Option Not defined

printf ("? n");

Break

Default

printf ("C is%dn", c);

Break

}

}

return 0;

}

Run Screenshots:

Description: Getopt_long_only, this function is the same as the Getopt_long, only can use '-' followed by the long option name, such as./main-username Jackie