[Reprinted] Programming tools under Linux

Argv = 0xBffFFFCA4, INIT = 0x80482bc <_init>, fini = 0x804845c <_fini>,

RTLD_FINI = 0x4000A350 <_dl_fini>, stack_end = 0xBfffffc9c)

at ../sysdeps/generic/libc-start.c:78

The output of the where command displays the call sequence of the function, the last function call, ie # 0 call is a C library

Function Gets. This function is called from the 11th row of Test.c (Main function).

4. Use the list command to view the code near the CENS function:

(GDB) List test.c: 11

6

7 int main ()

8 {

9

10 Printf ("Please Input A String:");

11 gets (string);

12

13 Printf ("/ NYOUR STRING IS:% S / N", String);

14}

15

5. The only factor that can cause a gets function error is the variable string. View String with the print command

Value:

(GDB) Print String

$ 1 = 0x0

Obviously, a null pointer is passed for the Gets function, which is the error of the program. This is because String is

A global variable, which is initialized to 0, an empty pointer.

6. In GDB, we can directly modify the value of the variable, just take the String a legal pointer value.

Yes, for this, we set breakpoints at the 11th line:

(GDB) BREAK 11

Breakpoint 1 at 0x8048408: File Test.c, Line 11.

(GDB) RUN

The Program Being Debugged Has Been Started ALREADY.

START IT from the basenning? (Y or n) y

Starting Program: / Home / Weiym / Projects / Study / GCC / TEST

Breakpoint 1, Main () at Test.c: 11

11 gets (string);

7. The program stopped until the 11th line, then we can use the set variable command to modify the String

Take the value:

(GDB) set var string = buff

8. Then continue to run, will see the correct program run:

(GDB) CONT

Continuing.

Please Input A String: Abcd

Your string is: abcd

Program evted with code 026.

The above example is sufficient to illustrate the general use of GDB, of course, the commands of GDB have a lot of commands, and can also be used to debug multi-threaded programs. The use of these commands requires readers to learn and master them in practice.

13.3.5 Version Control Tools

During the development of small software, use the Make tool to automatically complete some compilers. If it is involved

There are not many developers, and the maintenance of the code is simple. People usually use backup and mandatory code annotations to maintain the source

Order modification. However, in large projects, the developer and code are very large, it is necessary to use specialized

Version control software to maintain the revision of the code. In Microsoft's development tool, there is a SourceSafe

Software, specifically used to control, in large-scale development tools such as PowerBuilder, there is usually built-in

Version control system. On Linux, the usual version control system is called RCS, which Revision Control

System.

Using version control systems, developers can restore specific versions or revisions of a file when needed. In use

When the version control system, the developer's modification of a file is processed as follows:

1. When the developer has an initial source file version, archive the file into the version control system.

2. When the developer needs to modify a file, first get a copy of the current version. In a certain

When a developer gets a copy of the file, the version control system will ensure that other people cannot get the file.

3. When the dialog is modified, the developer saves the file as a new version.

4. This will then modify the file, will always be modified on the latest version of the file.

To this end, RCS provides many tools to help maintain the revision of source code, and the main tools are shown in Table 13-5.

Table 13-5 RCS main tools

Tool name

Features

Ci

Establish a new revision of a file or add a work file to the RCS file.

CO

Get a job version of a file for read-only purposes. (Co -l provides a working file and locking the original

This file can be modified. )

Ident

Search identifiers in the file.

Merge

Bring two files into the third file.

RCSDIFF

Compare the work files and RCS maintenance.

RCSMERGE

Merge of different versions of a file.

rlog

View the modification log of a file.

Limited to the space cannot explain the use of RCS in detail, please refer to the RCSINTRO (1) man page and the phase

Take help information.

13.3.6 Introduction to Perl

Linux provides developers with a vast event stage. Developers can not only use C / C , Fortran,

Pacal, Lisp and other programming language written programs, and can write programs in various scripting languages, including

Shell script, Perl script, TCL / TK script, etc. Usually, the scripting language is a programming language, but it

Close to natural language, with simple, convenient features, and in some ways, compared to traditional programming languages

More advantageous.

This section will briefly describe the scripting language Perl used in Linux. Perl, Practical

Extraction Report Language (Practical Reporting Report Language), created by Larry Wall, can be used from text

Decompose information in this document and use this information to establish a report. Due to Perl and Linux, it is also free soft.

Part, therefore, Perl is widely circulated in various computer systems. Various Linux business issued versions include Perl.

13.3.6.1 Execution of Perl scripts

Unlike traditional compilation languages, Perl scripts are generally some text files, interpreted by the Perl program and executed

Perl script. For example, the following is a simple Perl script:

#! / usr / bin / perl

# This is a comment.

Print "Hello, World! / N"

The first line of this script uses #! Specifies the explanation of the script as / usr / bin / perl, the second line is a note

Release, the third line print "Hello, World!".

Before performing this script, first set the script file to an executable mode. If the script name is Hello.pl

(.Pl is typically the suffix name of the Perl script), use the following command:

$ Chmod x hellol.pl

Then you can perform Hello.pl directly on the command line:

$ ./Hello.pl

In fact, Linux will execute the script as follows:

/ usr / bin / perl ./HELLO.PL

13.3.6.2 Basic syntax of Perl

Perl contains the same common features as other languages:

• Variables used to save different types of data.

• Expression of a combination of variables using an operator.

• Perform actions of action.

• Control the statement to execute the stream control statement of the route.

• Division function, provide functions of reusability (subroutines, or routines).

The writing form of the Perl program is free, and C is similar, each perl statement ends with a semicolon (;), # generation

Table A Note, Perl also defines a statement group with Co-Calbum ({...}).

The following section describes Perl variables, operators, and expressions, statements, stream controls, and other features.

13.3.6.3 variable

In the Perl program, you don't have to display the definition variables, all variables are headed by @, $ or%, representing Perl, respectively.

Three variable types.

• Scarr variable (SCALAR VARIABLE). Scalar type variable defines basic data types, including

Number, floating point and string. The scalar type variable begins with a character:

$ title = "Linux and windows nt";

$ count = 10;

• Array Variable. An array variable is a collection of scalar variables, array type variables

The prefix is ​​@, as shown below:

@commands = ("LS", "DIR", "CD", "RM", "MV");

@LENGTH = (2, 3, 2, 2, 2);

Elements in arrays can be accessed by a subscript method similar to a C language, for example:

$ comMMANDS [0]

• Associate array. Associated arrays are some collection of key / value, the keys

It is a string, and the value can be any scalar type variable. The prefix of the associated array is%. Use off

The association array can quickly find the corresponding value via a string key, as shown below:

% grades = ("WeiYM", 60, "zhengx", 100, "other", 50);

Use {key} to request the keys in the associated array: $ mygrade = $ grads {weiym}

It should be noted that in the statement, when the variable is in the dual quotation mark (""), Perl will evaluate the variable,

When the variable is in single quotation (''), Perl does not evaluate the variable. The following two statements will be different

content:

Print "My grade is $ grads [weiym] / n"; # output: my grade is 60

Print 'my grade is $ grads [weiym] / n'; # output: my grade is $ grads [weiym] / n

Perl has some predefined variables, including:

? @Argv: String array, contains a string option for scripts. ARGV ginseng similar to the C language main function

number.

?% EVN: Associated an associated array containing environment variables. For example, $ evN {home} is the user's home directory.

? $$: Process ID of the script.

$ <: The user ID of the script is run.

? $ ?: Near the return status of a system call.

$ _: The default parameters of many functions.

$ 0: Script Name.

13.3.6.4 Operators and Expressions

The operator is used to combine and compare the Perl variables, and Perl provides almost a operator like C. Including

, -, *, / and other arithmetic operators, and>, <,> =, <=, ==, etc., [] actual

Is the index operator of Perl.

However, the operator defined by the C language is very basic, we cannot compare strings with operators such as ==. In Perl

Also, in order to compare the string, Perl defines the two strings to compare two strings similar to the Fortran operator EQ.

Whether equal:

IF ($ INPUT EQ "quit") {

EXIT;

}

Other comparisons similar to Fortran are: ne (not equal), LT (less), GT (greater than), Le (less than or

Aliquot, GE (greater than or equal). You can also use the CMP operator to compare the string, will return -1, 0, 1 equivalent,

The return value is similar to the return value of the C function STRCMP.

Other unique operators provided by Perl are:

? **: Index operator, such as:

$ y ** = 2;

(): Empty number operator, can be used to initialize array variables, such as:

@Commands = ();

?: String Connection Operator, can be used to connect two string variables, such as:

$ Message = $ part1. $ part2;

• X =: Dress operator, can use the operator to repeat the number of times specified by the string, such as:

$ marker = "*";

$ marker x = 80; # $ maker will contain 65 *

? ..: Range Operators, can be used to easily initialize strings using this operator, such as:

$ alphabet = ('a' .. 'z'); in Chapter VII, we understand the regular expression. In Perl, regular expressions have been widely used.

E.g:

IF ($ name = ~ / [ww] ei [yy] [mm] /) {

Print "$ name is a bad man./N";

}

The print statement will be performed when "weiym" or "weiym" will be taken in $ NAME. Note that in the above statement, regular expression

Enclosed by / /, check if it matches, uses = ~ operators (check when not matching, using! ~ Operator).

13.3.6.5 Flow control statement

Perl provides the same stream control statement as the C language and contains some extra features. Perl conditions

The form of statements is as follows:

Conditional-statement {

Perl Code to Execute if Conditional IS TRUE

}

Note that the braces that enclose the execution code must exist, this point and C language is different. It is worth pointing out that Perl

Like C, regard any non-zero value as true, and see zero as False.

Table 13-6 briefly gives the flow control statement of Perl.

Table 13-6 Flow control statement of Perl and its use

Stream control statement

Description

Example

IF

Similar to the IF statement of the C language. Elseif

And ELSE clauses.

IF ($ USER EQ "root") {

Print "The Super User./N";

} else {

Print "a Normal User./N";

}

Unless

The same use as the IF statement, including Elseif and

ELSE clause. Its judgment results are the opposite of IF.

Unless ($ USER EQ "root") {

Print "a Normal User./N";

}

While

Similar to the WHILE statement in the C language. And C language

The Break and Continue statements correspond to the respective respective

Last and NEXT statements.

While () {

Print $ _;

}

for

Similar to the C language for statement syntax.

For ($ I = 0, $ SUM = 0; $ I <= 10; $ i ) {

$ SUM = $ i;

}

Foreach

Can be used to handle a special for statement of an array.

Foreach $ I (1..10) (

$ SUM = $ I;

}

goto

The use of the GOTO statement is the same as the C language.

REDO:

IF () {

Print $ _;

Goto Redo;

}

13.3.6.6 Access System

Perl can execute the Linux command by the following channels:

? Call the system to pass the Linux command to be executed.

• Specify the Linux command in a pair of demo (`).

Call the Fork function, similar to the Linux's Fork system call. Will copy the current script and in sub-process

Process new commands.

• Call the Exec function, similar to the EXEC system call for Linux. Will now overwrite the current script or command

script.

• Use Fork and Exec to provide a function similar to the shell (via the child process to monitor the user's input and

Handle the user command).

We will give an example in order to explain the last command execution pathway, see Listing 13-5.

Listing 13-5 psh.pl - use fork and exec to perform user commands ------------------------------- --------

#! / usr / bin / perl

# This script uses "fork" and "EXEC"

# To perform commands typed by users

$ prompt = "Command (/" exit / "to quit):";

Print $ PROMPT;

While () {

Chop; # 清除 / / /

IF ($ _ EQ "EXIT") {exit 0;}

$ status = for;

IF ($ status) {

# This is a parent process, waiting for the sub-process to end

Wait;

Print $ PROMPT;

NEXT;

} Else {

Exec $ _;

}

}

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

Execute the above script will result in the following results:

[Weiym @ versa perl] $ ./psh.pl

Command ("exit" to quit): PS

PID TTY TIME CMD

670 PTS / 1 00:00:00 Bash

807 PTS / 1 00:00:00 psh.pl

808 PTS / 1 00:00:00 PS

Command ("exit" to quit): EXIT

13.3.6.7 file processing

As you can see from the previous example, Perl uses stdin as the identifier of the standard input. In Perl,

The file is represented by the handle, usually used in uppercase. In addition to stdin, there are two predefined files in Perl.

The handle, that is, Stdout and STDERR, represent the standard output device and the error output device, respectively.

If you want to use another file, you can use the Open function to open the file, close the file with the Close function,

And use to read a line from a file. E.g:

Open (pwdfile, "/ etc / passwd);

While () {print $ _;}

Close Pwdfile;

13.3.6.8 User Custom Rollers

Perl contains a lot of built-in functions, but users can customize routines. Use in Perl scripts

The routine is very simple:

#! / usr / bin / perl

Sub Display

{

# Copy the function parameters to local variables

Local ($ Name, $ x) = @_;

Print "Grade of $ Name IS $ x / n";

}

% grades = ("WeiYM", 60, "zhengx", 100, "other", 50);

& Display ("WeiYM", $ grades {weiym});

& Display ("ZHENGX", $ grades {zhengx});

& Display ("Other", $ grades {oo};

The results of the above scripts are as follows:

[Weiym @ Versa Perl] $ ./grad.pl

Grade of weiym is 61

Grade of zhengx IS 100

Grade of Other IS 50

Perl provides users with more than 160 built-in functions, some of which are functions in the C standard library function, and others are functions for accessing the operating system. See the Perlfunc manual for details on the built-in function.

page. Other information about Perl is also divided into separate manuals, and summary information can be referred to in the Perl man page.

13.4 related programming style

The purpose of writing this section is to remind the reader to pay attention to the programming style during the programming process. If you are just writing some

The small exercise program, the program is only one or two hundred years of long, the programming style may not be important. However, if you and a lot

People develop work together, or, you want to understand your own procedures after a while,

It is necessary to develop good programming habits. In many programming habits, the programming style is the most important thing.

Good programming style can help developers in many ways. If you read Linux kernel source code

If you may pour a beautiful proof of the program. A good programming style can increase the readability of the code and help you

Ruand the head. If the program is very messy, it will give you a halo. The programming style is best to reflect one

Programmer's overall quality.

However, if you compare the programs under both Windows and Linux, it will be found in the programming style.

Two systems have a relatively large difference.

Many readers may be familiar with Hungarian nomenclature respected by Windows. This method is defined very complex

Named methods of functions, variables, types, etc.

Name, use the added prefix to represent its type, for example:

Char szbuffer [20];

Int ncount;

Use SZ and N to represent strings and integers, respectively. In order to represent a variable name, the following variable name is used.

possible:

Int IthisaverylongVariable;

In Win32API, functions with complex names and calling parameters are uncommon, for example:

Bool GetSecurityDescriptorControl

Psecurity_descriptor PsecurityDescriptor,

Psecurity_Descriptor_control pcontrol,

LPDWORD LPDWREVISION;

In Linux, we often see that the definition is a very simple function interface and variable name. In Linux

In the source code of the core, you can see the encoding style of Linux kernel source code ( /

Documentation / CodingStyle). We have repeatedly mentioned the exquisite characteristics of UNIX systems and the building blocks.

Plan the principle. C language originated from the UNIX operating system, like UNIX design principles, C language is widely recognized

An important reason for use is its flexibility and simplicity. Therefore, when writing programs with C language, start

It should eventually meet its simple design principles without using a very complex variable naming method. Linus is Linux

Nuclear defined C language coding style points are as follows:

1. When indent, use a length of 8 characters wide. If the procedure has more than 3,

Through the redesign program.

2. Brand position. In addition to the definition of the function, the left brage should be placed in the end of the row, and the right brace is placed.

In the lead. The definition body of the function should be placed on the lead. As follows:

Int Function (int x, int y)

{

IF (x == y) {

...

} Else if (x> y) {

...

} Else {

...

}

Return 0;

}

3. A concise naming method should be used. For the variable name, do not agree with the form of case in cases, but encourage use

Descriptive name; not using global variables as much as possible; non-use of the Hungarian nomenclature to indicate the type of variable;

The fine name represents a partial variable; keep the function short, avoiding too much local variables.

4. Keep the function short.

5. The role of the annotation should not be excessively emphasized, should try to use a good coding style rather than adding too much comments.

13.5 small knot

In many ways, Linux and Windows NT are different in many ways, and this chapter is from the operating system.

The interface starts, simply compare Linux and Windows NT in system interface, function library, programming tool, and encoding

Different from style. Considering that many readers will carry out application software development on Linux, this chapter

I have explained the development tools mainly used when software development on Linux, including:

? GNU C, C compiler

? GNU Make Tool

? GNU debugger

? RCS version control system

This chapter also briefly introduces the popular Perl scripting language on Linux systems.

In fact, the concept of programming is everywhere in Linux systems, and many tools provide similar programming languages.

Variable definition, grammar, rules, etc. Therefore, the Linux system provides programmers with a broader stage.

Regardless of Linux or on Windows NT, graphical user interface programming is a very heavy in software development.

The topic you want. The next chapter will focus on the X Window software development on Linux and the application of Windows NT.

A comparison of the development of a piece.