Home > Articles > Data > MySQL

Using the MySQL Client Library to Write Your Own Programs

  • Print
  • + Share This
Write your own client programs in C with the MySQL Client Library. Follow these guidelines to maintain consistency with existing client programs in the MySQL distribution, as well as modularity and reusability of your code. Create a series of programs from a simple server connection to an interactive query.
This chapter is from the book

This chapter is from the book

MySQL provides a client library written in the C programming language that you can use to write client programs that access MySQL databases. This library defines an application programming interface that includes the following facilities:

  • Connection management routines to establish and terminate a session with a server.

  • Routines to construct queries, send them to the server, and process the results.

  • Status- and error-reporting functions for determining the exact reason for an error when other C API calls fail.

This chapter shows how to use the client library to write your own programs. Some of the goals we'll keep in mind are consistency with existing client programs in the MySQL distribution, as well as modularity and reusability of the code. I assume you know something about programming in C, but I've tried not to assume you're an expert.

The chapter develops a series of client programs in a rough progression from very simple to more complex. The first part of this progression develops the framework for a client skeleton that does nothing but connect to and disconnect from the server. The reason for this is that although MySQL client programs are written for different purposes, they all have one thing in common: They establish a connection to the server.

We'll build the skeleton in steps:

  1. Write some bare-bones connection and disconnection code (client1).

  2. Add error checking (client2).

  3. Make the connection code modular and reusable (client3).

  4. Add the ability to get connection parameters (host, user, password) at runtime (client4).

This framework is reasonably generic, and you can use it as the basis for any number of client programs. After developing it, we'll pause to consider how to handle various kinds of queries. Initially, we'll discuss how to handle specific hardcoded SQL statements, then develop code that can be used to process arbitrary statements. After that, we'll add our query-processing code to our client framework to develop another program (client5) that's similar to the mysql client.

We'll also consider (and solve) some common problems, such as, "How can I get information about the structure of my tables" and "How can I insert images in my database?"

This chapter discusses functions and data types from the client library only as they are needed. For a comprehensive listing of all functions and types, see Appendix F, "C API Reference." You can use that appendix as a reference for further background on any part of the client library you're trying to use.

The example programs are available online for downloading so you can try them directly without typing them in yourself. See Appendix A, "Obtaining and Installing Software," for instructions.

Where to Find Examples

A common question on the MySQL mailing list is "Where can I find some examples of clients written in C?" The answer, of course, is "right here in this book!" But something many people seem not to consider is that the MySQL distribution contains several client programs (mysql, mysqladmin, and mysqldump, for example), most of which are written in C. Because the distribution is readily available in source form, MySQL itself provides you with quite a bit of example client code. Therefore, if you haven't already done so, grab a source distribution sometime and take a look at the programs in the client directory. The MySQL client programs are in the public domain and you may freely borrow code from them for your own programs.

Between the examples provided in this chapter and the client programs included in the MySQL distribution, you may be able to find something similar to what you want to do when writing your own programs. If you do, you may be able to reuse code by copying an existing program and modifying it. You should read this chapter to gain an understanding of how the client library works. Remember, however, that you don't always need to write everything yourself from the ground up. (You'll notice that code reusability is one of the goals in our discussion of writing programs in this chapter.) If you can avoid a lot of work by building on what someone else has already done, so much the better.

General Procedure for Building Client Programs

This section describes the steps involved in compiling and linking a program that uses the MySQL client library. The commands to build clients vary somewhat from system to system, and you may need to modify the commands shown here a bit. However, the description is general and you should be able to apply it to almost any client program you write.

Basic System Requirements

When you write a MySQL client program in C, you'll need a C compiler, obviously. The examples shown here use gcc. You'll also need the following in addition to your own source files:

  • The MySQL header files

  • The MySQL client library

The MySQL header files and client library constitute client programming support. They may be installed on your system already. Otherwise, you need to obtain them. If MySQL was installed from a source or binary distribution, client programming support should have been installed as part of that process. If MySQL was installed from RPM files, this support won't be present unless you installed the developer RPM. If you need to install the MySQL header files and library, see Appendix A.

Compiling and Linking the Client

To compile and link a client program, you must specify where the MySQL header files and client library are located because they usually are not installed in locations that the compiler and linker search by default. For the following example, suppose the header file and client library locations are /usr/local/include/mysql and /usr/local/lib/mysql.

To tell the compiler how to find the MySQL header files, pass it a -I/usr/local/include/mysql argument when you compile a source file into an object file. For example, you might use a command like this:

% gcc -c -I/usr/local/include/mysql myclient.c

To tell the linker where to find the client library and what its name is, pass -L/usr/local/lib/mysql and -lmysqlclient arguments when you link the object file to produce an executable binary, as follows:

% gcc -o myclient myclient.o -L/usr/local/lib/mysql -lmysqlclient

If your client consists of multiple files, name all the object files on the link command. If the link step results in an error having to do with not being able to find the floor() function, link in the math library by adding -lm to the end of the command:

% gcc -o myclient myclient.o -L/usr/local/lib/mysql -lmysqlclient -lm

You might need to add other libraries as well. For example, you'll probably need -lsocket -lnsl on Solaris.

If you don't use make to build programs, I suggest you learn how so that you won't have to type a lot of program-building commands manually. Suppose you have a client program, myclient, comprising two source files, main.c and aux.c, and a header file, myclient.h. A simple Makefile to build this program might look like this:

CC = gcc
INCLUDES = -I/usr/local/include/mysql
LIBS = -L/usr/local/lib/mysql -lmysqlclient

all: myclient

main.o: main.c myclient.h
  $(CC) -c $(INCLUDES) main.c
aux.o: aux.c myclient.h
  $(CC) -c $(INCLUDES) aux.c

myclient: main.o aux.o
  $(CC) -o myclient main.o aux.o $(LIBS)

clean:
  rm -f myclient main.o aux.o

If your system is one for which you need to link in the math library, change the value of LIBS to add -lm to the end:

LIBS = -L/usr/local/lib/mysql -lmysqlclient -lm

If you need other libraries, such as -lsocket and -lnsl, add those to LIBS, too.

Using the Makefile, you can rebuild your program whenever you modify any of the source files simply by typing "make". That's easier and less error prone than typing a long gcc command.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020