Writing and Compiling C Program in Linux Part 3: Using Makefile

Compiling C Program using Make

• Using the example in Part 2, instead of compiling line by line, we can create a make file that will follow certain compiling instructions.
• The format for the make file is:

target: dependencies

command

• The file is usually called Makefile
• The Makefile of previous tvm program will be as follows:

#Creating object

tvm2: tvm2.o finlib.o

gcc tvm2.o finlib.o -lm -o tvm2

tvm2.o: tvm2.c fin.h

gcc -c tvm2.c

finlib.o: finfn.c fin.h

gcc -c finfn.c -o finlib.o

clean:

rm -f tvm2 tvm2.o finlib.o

• This is the more explicit way to instruct the make program how to compile line by line.
• Please note that the final program must come first before compilation of object. It is a drill down approach.
• After the make file is written, you can package all the program and Makefile together.
• To compile the program just type #make
• To remove the compiled program and object type #make clean
• However, we need not be so explicit because make program know how to compile programs.
• See the example below:

CFLAGS=-Wall

LDFLAGS=-lm

#Creating object

tvm: tvm.o finfn.o fin.h

clean:

rm -f tvm tvm.o finfn.o

• CFLAGS refers to compile flags
• LDFLAGS refers to linking flags
• By indicating our target program and the dependencies, the make program will compile the program and link them appropriately using the flags indicated.
• Since the custom library need not compile every time, we can include the main C program and the object file of the library.
• The Makefile will be slightly different, as follows:

CFLAGS=-Wall

LDFLAGS=-lm

#Creating object

tvm: tvm.o finlib.o fin.h

clean:

rm -f tvm tvm.o

• We don’t supply finfn.c but we supply a precompiled object file finlib.o.

Writing and Compiling C Program in Linux Part 2: Using Custom Library

• Instead of building custom function in a C program, we can include any custom function into a custom library. In this way, we could reuse the custom function between different program.
• First, we maintain the same main(), but we remove all custom financial functions. Instead we included a statement included “fin.h” so that the compiler will search for the header file.

#include <stdio.h>

#include "fin.h"

int main (void)

{

double myrate;

int myterm;

double myprincipal;

double myreturn;

printf ("Please enter the following:\n");

printf ("Rate of return:(In decimal 50%% is 0.5)");

scanf ("%lf", &myrate);

printf ("\n");

printf ("Number of terms:(No decimals): ");

scanf ("%d", &myterm);

printf ("\n");

printf ("The principal amount: ");

scanf ("%lf", &myprincipal);

printf ("\n");

myreturn = tvm (myrate, myterm, myprincipal);

printf ("Your return after %d term is $%.2lf.\n", myterm, myreturn);

return 0;

}

• Next, we create a header file (“fin.h”) that will include all financial functions in the future.

double tvm (double rate, int terms, double principal);

• Finally, we create a new program call finfn.c (as in financial function). The custom function will be place here.

#include <math.h>

#include "fin.h"

double tvm (double rate, int terms, double principal)

{

double dn;

double pp;

dn = terms;

pp = pow (1+rate, dn);

return principal * pp;

}

• The purpose splitting the program is such that tvm function can be reuse as a custom library in another program.
• We can compile all the program #gcc -Wall tvm.c finfn.c -o tvm –lm
• However, we don’t have to compile finfn.c every time of there is no changes.
• One way is to create an object file during compilation instead of create executable.
• We compile finfn.c first: #gcc -Wall -c finfn.c -o finlib.o
• With the object file available, we can create another program tvm2 using the same tvm function:

#include <stdio.h>

#include "fin.h"

int main (void)

{

double rate = 0.025;

int term = 10;

double principal = 1000;

double result = 0;

result = tvm (rate, term, principal);

printf ("The return of $1000 investment with a rate of 2.5 percent in 10 years will give you $%.2lf.\n", result);

return 0;

}

• Then we compile tvm2.c first before linking:

#gcc -Wall -c tvm2.c -o tvm2.o

• We can link both program as follows:

#gcc tvm.o finlib.o -lm -o tvm

#gcc tvm2.o finlib.o -lm -o tvm2

• In the example, we compile 2 programs using the custom function in one object file.
• Alternatively, we can compile straight from tvm2.c to executable like below:

#gcc -Wall tvm2.c finlib.o -lm -o tvm2

Writing and Compiling C Program in Linux GCC Part 1

• GCC compiler is usually installed together with your Linux. If not, use the command $sudo apt-get install gcc (for Ubuntu user) and #yum install gcc (for Fedora, Redhat user). For Fedora user, you need to be in su mode before installation.
• Below is a simple C program called sick.c

#include <stdio.h>

int main(void)

{

printf ("Sick of printing hello!\n");

return 0;

}

• To compile the program #gcc -Wall sick.c -o verysick
• The option -Wall display all possible Warning and -o indicate to the compiler that user want the output to be name after the -o option.
• To run the program indicate the complete path or $./verysick

Writing and Compiling C Program using Math Library

• Below is a more complex C program called tvm.c

#include <stdio.h>

#include <math.h>

double tvm (double rate, int terms, double principal);

int main (void)

{

double myrate;

int myterm;

double myprincipal;

double myreturn;

printf ("Please enter the following:\n");

printf ("Rate of return:(In decimal 50%% is 0.5) ");

scanf ("%lf", &myrate);

printf ("\n");

printf ("Number of terms:(No decimals): ");

scanf ("%d", &myterm);

printf ("\n");

printf ("The principal amount: ");

scanf ("%lf", &myprincipal);

printf ("\n");

myreturn = tvm (myrate, myterm, myprincipal);

printf ("Your return after %d term is $%.2lf.\n", myterm, myreturn);

return 0;

}

double tvm (double rate, int terms, double principal)

{

double dn;

double pp;

dn = terms;

pp = pow (1+rate, dn);

return principal * pp;

}

• To compile the program #gcc -Wall tvm.c -lm -o tvm
• The additional option -lm is required so that the compiler will search for the math library in reference to including math.h.