Encyclopedia of C language functions — functions starting with x (2)

C language function collection

This article introduces the complete set of C language functions — functions starting with x

1. xdr_char

1.1 Function Description

Function declaration	Function function
`bool_t xdr_char(XDR xdrs, char cp);`	for Encode a `char` type data into `XDR` stream or decode a `char` type data from `XDR` stream

Parameters:

xdrs : Pointer to the XDR structure to encode or decode data

cp: Pointer to char type data to be encoded or decoded

Return value:

If the encoding or decoding is successful, the return value is TRUE;

Otherwise the return value is FALSE.

1.2 Demonstration example

#include <stdio.h>
#include <rpc/xdr.h>

int main()
{<!-- -->
    // create XDR stream
    XDR xdr;
    xdrmem_create( & xdr, NULL, 0, XDR_ENCODE);

    // write char value
    char c = 'A';
    if (!xdr_char( &xdr, &c))
    {<!-- -->
        printf("Write failed");
        return 1;
    }

    // reset XDR stream to decoding mode
    xdrrec_endofrecord( & xdr, true);

    // read char value from stream
    char result;
    if (!xdr_char( &xdr, &result))
    {<!-- -->
        printf("Failed to read");
        return 1;
    }

    // output result
    printf("Read result: %c\\
", result);
    return 0;
}

In the sample code above,

First, we call the xdrmem_create() function to create a XDR stream;
Then, use the xdr_char() function to write the char value to the stream;
Next, reset the stream to decode mode by calling the xdrrec_endofrecord() function;
Then, use the xdr_char() function to read the char value from the stream;
Finally, output the char value read from the stream.

2. xdr_callmsg

2.1 Function Description

Function declaration	Function function
`bool_t xdr_callmsg(XDR xdrs, struct rpc_msg cmsg);`	used Used to encode a structure representing a `RPC` message into an `XDR` stream or decode a `RPC` stream from a `XDR` stream The structure of the message

Parameters:

xdrs : A pointer to an XDR structure to encode or decode data

cmsg : Pointer to a structure representing the RPC message

Return value:

If the encoding or decoding is successful, the return value is TRUE;

Otherwise the return value is FALSE.

2.2 Demonstration example

#include <stdio.h>
#include <rpc/xdr.h>
#include <rpc/rpc.h>

int main()
{<!-- -->
    // Create a structure representing the RPC message
    struct rpc_msg cmsg = {<!-- -->
        .rm_xid = 1234567890,
        .rm_direction = CALL,
        .rm_call.cb_rpcvers = 2,
        .rm_call.cb_prog = 100001,
        .rm_call.cb_vers = 1,
        .rm_call.cb_proc = 4
    };
    
    // create XDR stream
    XDR xdr;
    char buffer[1024];
    xdrmem_create( & xdr, buffer, sizeof(buffer), XDR_ENCODE);

    // encode the message into the XDR stream
    if (!xdr_callmsg( &xdr, &cmsg))
    {<!-- -->
        printf("Encoding failed");
        return 1;
    }

    // reset XDR stream to decoding mode
    xdrrec_endofrecord( & xdr, true);

    // read message from stream
    struct rpc_msg result;
    if (!xdr_callmsg( &xdr, &result))
    {<!-- -->
        printf("Decoding failed");
        return 1;
    }

    // output result
    printf("Read result:\\
");
    printf(" XID: %u\\
", result.rm_xid);
    printf("Direction: %d\\
", result.rm_direction);
    printf("RPC Version: %u\\
", result.rm_call.cb_rpcvers);
    printf("Program: %u\\
", result.rm_call.cb_prog);
    printf("Program Version: %u\\
", result.rm_call.cb_vers);
    printf(" Procedure: %u\\
", result.rm_call.cb_proc);
    
    return 0;
}

In the example above,

First, we define a structure cmsg representing the RPC message, which contains the XID of the message, the direction, Fields such as RPC version number, program number, program version number, and procedure number.
Next, use the xdrmem_create() function to create an in-memory XDR stream for encoding messages into XDR format;
Then, call the xdr_callmsg() function to encode the message into the XDR stream. If the encoding is successful, the return value is TRUE, otherwise the return value is FALSE.
Next, call the xdrrec_endofrecord() function to reset the stream to decode mode so that encoded messages can be read from the stream.
Then, call the xdr_callmsg() function again to decode a structure representing the RPC message from the stream, and save it in the result variable middle.
Finally, use the printf() function to output the decoded message fields.

3. xdr_double

3.1 Function Description

Function declaration	Function function
`bool_t xdr_authunix_parms(XDR xdrs, struct authunix_parms objp);`	use Used to encode `double` type data into `XDR` stream or decode a `double` type data from `XDR` stream td>

Parameters:

xdrs : A pointer to an XDR structure to encode or decode data

dp : Pointer to double type data to encode or decode

Return value:

If the encoding or decoding is successful, the return value is TRUE;

Otherwise the return value is FALSE.

3.2 Demonstration example

#include <stdio.h>
#include <rpc/xdr.h>

int main()
{<!-- -->
    // create XDR stream
    XDR xdr;
    char buffer[1024];
    xdrmem_create( & xdr, buffer, sizeof(buffer), XDR_ENCODE);

    // write double value
    double d = 3.1415926;
    if (!xdr_double( &xdr, &d))
    {<!-- -->
        printf("Write failed");
        return 1;
    }

    // reset XDR stream to decoding mode
    xdrrec_endofrecord( & xdr, true);

    // read a double value from the stream
    double result;
    if (!xdr_double( &xdr, &result))
    {<!-- -->
        printf("Failed to read");
        return 1;
    }

    // output result
    printf("Read result: %f\\
", result);
    return 0;
}

In the sample code above,

First, we call the xdrmem_create() function to create a XDR stream;
Then, use the xdr_double() function to write the double value to the stream;
Next, reset the stream to decode mode by calling the xdrrec_endofrecord() function;
Then, use the xdr_double() function to read the double value from the stream;
Finally, outputs the double value read from the stream.

Note: Extra care must be taken when using the xdr_double function, as different system architectures and endianness may affect how floating-point numbers are represented. It is recommended to only transfer between the same system and language when using this function.

4. xdr_enum

4.1 Function Description

Function declaration	Function function
`bool_t xdr_enum(XDR xdrs, enum_t ep);`	for Encode enumeration type data into `XDR` stream or decode enumeration type data from `XDR` stream

Parameters:

xdrs : A pointer to an XDR structure to encode or decode data

ep: A pointer to the enumerated type data to be encoded or decoded

Return value:

If the encoding or decoding is successful, the return value is TRUE;

Otherwise the return value is FALSE.

4.2 Demonstration example

#include <stdio.h>
#include <rpc/xdr.h>

enum Color
{<!-- -->
    RED,
    GREEN,
    BLUE
};

int main()
{<!-- -->
    // create XDR stream
    XDR xdr;
    char buffer[1024];
    xdrmem_create( & xdr, buffer, sizeof(buffer), XDR_ENCODE);

    // write enum type value
    enum Color c = GREEN;
    if (!xdr_enum( & amp;xdr, (enum_t *) & amp;c))
    {<!-- -->
        printf("Write failed");
        return 1;
    }

    // reset XDR stream to decoding mode
    xdrrec_endofrecord( & xdr, true);

    // read the enum type value from the stream
    enum Color result;
    if (!xdr_enum( & amp;xdr, (enum_t *) & amp;result))
    {<!-- -->
        printf("Failed to read");
        return 1;
    }

    // output result
    printf("Read result: %d\\
", result);
    return 0;
}

In the example program above,

First, we call the xdrmem_create() function to create a XDR stream;
Then, use the xdr_enum() function to write the enum type value GREEN to the stream;
Then, call the xdrrec_endofrecord() function to reset the stream to decoding mode;
Then, use the xdr_enum() function to read the enumeration type value from the stream;
Finally, the printf() function is called to output the Boolean value read from the stream.

5. xdr_float

5.1 Function Description

XDR stream >

Function declaration	Function function
`bool_t xdr_float(XDR xdrs, float fp);`	for Encode `float` type data into `XDR` stream or decode a `float` type data

Parameters:

xdrs : A pointer to an XDR structure to encode or decode data

fp : Pointer to float type data to encode or decode

Return value:

If the encoding or decoding is successful, the return value is TRUE;

Otherwise the return value is FALSE.

5.2 Demonstration example

#include <stdio.h>
#include <rpc/xdr.h>

int main()
{<!-- -->
    // create XDR stream
    XDR xdr;
    char buffer[1024];
    xdrmem_create( & xdr, buffer, sizeof(buffer), XDR_ENCODE);

    // write float value
    float f = 3.14;
    if (!xdr_float( &xdr, &f))
    {<!-- -->
        printf("Write failed");
        return 1;
    }

    // reset XDR stream to decoding mode
    xdrrec_endofrecord( & xdr, true);

    // read float value from stream
    float result;
    if (!xdr_float( &xdr, &result))
    {<!-- -->
        printf("Failed to read");
        return 1;
    }

    // output result
    printf("Read result: %f\\
", result);
    return 0;
}

In the sample code above,

First, we call the xdrmem_create() function to create a XDR stream;
Then, use the xdr_float() function to write the float value to the stream;
Next, reset the stream to decode mode by calling the xdrrec_endofrecord() function;
Then, use the xdr_float() function to read the float value from the stream;
Finally, output the float value read from the stream.

6. xdr_free

6.1 Function Description

Function declaration	Function function
`void xdr_free(xdrproc_t proc, char* objp);`	for release Dynamic memory space allocated by xdr series functions

Parameters:

proc : The pointer type of the serialized or deserialized object

objp: A pointer to dynamically allocated memory that needs to be freed

6.2 Demonstration example

#include <stdio.h>
#include <rpc/xdr.h>

struct Person {<!-- -->
    char *name;
    int age;
};

int main()
{<!-- -->
    // create XDR stream
    XDR xdr;
    char buffer[1024];
    xdrmem_create( & xdr, buffer, sizeof(buffer), XDR_ENCODE);

    // allocate memory and encode data into XDR stream
    struct Person *p = (struct Person *)xdr_malloc( & xdr, sizeof(struct Person));
    p->name = "Huazie";
    p->age = 18;
    xdr_struct( & amp; xdr, "Person", (xdrproc_t)xdr_person, (char *)p);
    xdr_free((xdrproc_t)xdr_person, (char *)p);

    // reset XDR stream to decoding mode
    xdrrec_endofrecord( & xdr, true);

    // decode data and free memory
    struct Person result;
    if (xdr_struct( &xdr, "Person", (xdrproc_t)xdr_person, (char *) &result))
    {<!-- -->
        printf("Read result: name = %s, age = %d\\
", result.name, result.age);
        xdr_free((xdrproc_t)xdr_person, (char *) &result);
    }
    else
    {<!-- -->
        printf("Failed to read");
    }

    return 0;
}

// Encode and decode Person type data
bool_t xdr_person(XDR *xdrs, struct Person *p)
{<!-- -->
    return xdr_string(xdrs, & amp;p->name, ~0) & amp; & amp; xdr_int(xdrs, & amp;p->age);
}

In the sample code above,

First, a structure named Person is defined, which contains a name field of string type and an age field of integer type ;
Then, we use the xdrmem_create() function to create a XDR stream and bind it to the buffer buffer;
Next, we call the xdr_malloc() function to allocate the memory space of a structure Person, and assign name to "Huazie\ ", age is 18;
Then, call the xdr_struct() function to encode the above structure data into the XDR stream. After the encoding is completed, call the xdr_free() function to release the allocated memory space, so that the dynamically allocated memory space used in the serialization process can be released.
Next, we reset the XDR stream to decode mode;
Then, use the xdr_struct() function to read and decode data from the stream. If the decoding is successful, the result is stored in a Person structure called result . After decoding, we use the xdr_free() function to release the dynamically allocated memory space.
Finally, output the name and age field values in the Person structure.

7. xdr_hyper

7.1 Function Description

Function declaration	Function function
`bool_t xdr_hyper(XDR xdrs, hyper hp);`	for Encode and decode data of super long integer type

Parameters:

xdrs : A pointer to an XDR structure to encode or decode data

hp: Pointer to the long integer type to encode or decode

Return value:

If the encoding or decoding is successful, the return value is TRUE;

Otherwise the return value is FALSE.

7.2 Demonstration example

#include <stdio.h>
#include <rpc/xdr.h>

int main()
{<!-- -->
    // create XDR stream
    XDR xdr;
    char buffer[1024];
    xdrmem_create( & xdr, buffer, sizeof(buffer), XDR_ENCODE);

    // Encode data of super long integer type
    hyper h = 1234567890123456789;
    if (xdr_hyper( &xdr, &h))
    {<!-- -->
        printf("encoded successfully\\
");
    }

    // reset XDR stream to decoding mode
    xdrrec_endofrecord( & xdr, true);

    // Decode data of super long integer type
    hyper result;
    if (xdr_hyper( &xdr, &result))
    {<!-- -->
        printf("Decoding succeeded, result = %lld\\
", result);
    }

    return 0;
}

In the sample code above,

First, we use the xdrmem_create() function to create a XDR stream and bind it to the buffer buffer;
Then, define a variable h of super long integer type, and assign it as 1234567890123456789;
Then, use the xdr_hyper() function to encode the data of the super long integer type into the XDR stream, and check whether the encoding is successful; if the encoding is successful, output \ "Encoding successful";
Then, call the xdrrec_endofrecord() function to reset the XDR stream to decoding mode;
Finally, call the xdr_hyper() function to decode the data read from the XDR stream into a super long integer type, and check whether the decoding is successful; if the decoding is successful, output the decoded result.

8. xdr_int

8.1 Function Description

XDR stream >

Function declaration	Function function
`bool_t xdr_int(XDR xdrs, int ip);`	for Encode `int` type data into `XDR` stream or decode a `int` type data

Parameters:
Parameters:

xdrs : A pointer to an XDR structure to encode or decode data

ip : Pointer to int type data to encode or decode

Return value:

If the encoding or decoding is successful, the return value is TRUE;

Otherwise the return value is FALSE.

8.2 Demonstration example

#include <stdio.h>
#include <rpc/xdr.h>

int main()
{<!-- -->
    // create XDR stream
    XDR xdr;
    char buffer[1024];
    xdrmem_create( & xdr, buffer, sizeof(buffer), XDR_ENCODE);

    // Encode integer type data
    int i = 12345;
    if (xdr_int( &xdr, &i))
    {<!-- -->
        printf("encoded successfully\\
");
    }

    // reset XDR stream to decoding mode
    xdrrec_endofrecord( & xdr, true);

    // decode integer type data
    int result;
    if (xdr_int( &xdr, &result))
    {<!-- -->
        printf("Decoding succeeded, result = %d\\
", result);
    }

    return 0;
}

In the sample code above,

First, we call the xdrmem_create() function to create a XDR stream;
Then, use the xdr_int() function to write the value 12345 of type int to the stream; if it returns TRUE, Then it means that the encoding is successful, output "encoding success";
Next, reset the stream to decode mode by calling the xdrrec_endofrecord() function;
Finally, use the xdr_int() function to read the value of the int type from the stream; if it returns TRUE, it means that the decoding is successful, and the read from the stream is output A value of type int.

9. xdr_long

9.1 Function Description

XDR stream >

Function declaration	Function function
`bool_t xdr_long(XDR xdrs, long lp);`	for Encode `long` type data into `XDR` stream or decode a `long` type data

Parameters:

xdrs : A pointer to an XDR structure to encode or decode data

lp: Pointer to data of type long to encode or decode

Return value:

If the encoding or decoding is successful, the return value is TRUE;

Otherwise the return value is FALSE.

9.2 Demonstration example

#include <stdio.h>
#include <rpc/xdr.h>

int main()
{<!-- -->
    // create XDR stream
    XDR xdr;
    char buffer[1024];
    xdrmem_create( & xdr, buffer, sizeof(buffer), XDR_ENCODE);

    // Encode data of long integer type
    long l = 1234567890;
    if (xdr_long( &xdr, &l))
    {<!-- -->
        printf("encoded successfully\\
");
    }

    // reset XDR stream to decoding mode
    xdrrec_endofrecord( & xdr, true);

    // Decode data of long integer type
    long result;
    if (xdr_long( &xdr, &result))
    {<!-- -->
        printf("Decoding succeeded, result = %ld\\
", result);
    }

    return 0;
}

In the sample code above,

First, we call the xdrmem_create() function to create a XDR stream;
Then, use the xdr_long() function to write the value 1234567890 of type long to the stream; if it returns TRUE, Then it means that the encoding is successful, output "encoding success";
Then, call the xdrrec_endofrecord() function to reset the stream to decoding mode;
Finally, use the xdr_long() function to read the value of the long type from the stream; if it returns TRUE, it means that the decoding is successful, and the read from the stream is output A value of type long.