6/9/2016Course material created by D. Woit 1 CPS 393 Introduction to Unix and C START OF WEEK 10 (C-4)

6/9/2016Course material created by D. Woit 2 Command line Processing main is a function--so OS can pass arguments to it using –Argument Vector, and –Argument Count int main(int argc, char *argv[]) suppose -make executable cla from cla.c: gcc -o cla cla.c -and execute as: cla abc "de f" 74 -then inside cla.c: argc is 4 // # args + 1 (#elts in argv) argv[0] is "cla" // program name argv[1] is "abc" // argument 1 argv[2] is "de f" // argument 2 argv[3] is "74" // argument 3

6/9/2016Course material created by D. Woit 3 Command line Processing Program could print its COMMAND LINE ARGUMENTS as follows: int main (int argc, char *argv[]) { int i; for (i=1; i<argc; i++) printf("command line argument %d is: %s\n", i, argv[i]); printf("Name of program is: %s\n", argv[0]); exit(0); }

6/9/2016Course material created by D. Woit 4 /*Source: suma.c Purpose: to sum the integers supplied on the command line Input: any number of integers in command line Output: the sum of the inputted numbers */ #include int main (int argc, char *argv[]) { int i, /*for loop index*/ sum=0; /*the sum of the arguments*/ for (i=1; i<argc; i++) { sum = sum + atoi(argv[i]); } printf("Sum of the %d integers is %d\n", argc-1, sum); exit(0); } HMWK: Fix suma.c so that it checks for good integer input

6/9/2016Course material created by D. Woit 5 /*Source: cml2.c Purpose: print max of 2 int arguments */ #define GoodInput 0 #define BadInput 1 #include int main (int argc, char *argv[]) { if (argc != 3 ) { fprintf(stderr, "Usage: %s int1 int2\n", argv[0]); exit(BadInput); } if (atoi (argv[1]) > atoi (argv[2]) ) fprintf(stdout, "%s\n", argv[1]); else fprintf(stdout, "%s\n", argv[2]); exit(GoodInput); } Note that functions strtof/strtod etc convert string to float/double etc

6/9/2016Course material created by D. Woit 6 File I/O already used fprintf/fputs to print to FILE stdout, stderr fprintf(stderr, "bad input: %d\n", x); Others: fscanf (fp, str, length) fgetc (fp); fputc (ch, fp) fgets (str, length, fp); fputs (str, fp);

6/9/2016Course material created by D. Woit 7 File I/O Open file named myfile for reading: FILE *fp; // FILE in stdio.h if ( (fp = fopen("myfile","r")) == NULL ) { fprintf(stderr,"fopen: Error opening file\n"); exit(1); } fscanf(fp, "%d", &i); Mode ---- r open text file for read w open text file for write a append to text file r+ open text file for r/w w+ create t.f. for r/w a+ append or create for r/w Note: w & w+: if file not exist, created if it exists, it is destroyed & new created

6/9/2016Course material created by D. Woit 8 Closing a file fclose(fp); 0 if successful EOF if not (exit *should* close all files before pgm termination). fgetc(fp); returns: char read if succ (cast to int) EOF otherwise fputc(ch,fp); returns: char written if succ (cast to int) EOF otherwise

6/9/2016Course material created by D. Woit 9 Example /*Source cio.c Purpose: write a string to file myfile */ #include #define GOOD 0 #define BAD 1 int main(void) { char str[40] = "String to write onto disk"; FILE *fp; char ch, *p; if ((fp = fopen("myfile","w"))==NULL) { fprintf(stderr,"fopen: Cannot open file\n"); exit(BAD); }

6/9/2016Course material created by D. Woit 10 p=str; while (*p) if (fputc(*p++,fp)==EOF) { fprintf(stderr,"fuptc: Error writing file\n"); fclose(fp); /*good form*/ exit(BAD); } fclose(fp); /*good form*/ exit(GOOD); }

6/9/2016Course material created by D. Woit 11 Example /*Source: cio2.c Purpose: display contents of myfile on stdout */ #include #define GOOD 0 #define BAD 1 int main(void) { FILE *fp; int ch; if ((fp=fopen("myfile", "r"))==NULL) { fprintf(stderr,"fopen: Cannot open file\n"); exit(BAD); } while (( ch = fgetc(fp)) != EOF) fputc(ch,stdout); fclose(fp); exit(GOOD); }

6/9/2016Course material created by D. Woit 12 HMWK: Modify cio2.c to turn it into a simple version of unix utility "cat". If no cmd-line input, prints stdin on stdout. If cmd-line inputs (files), print each on stdout

6/9/2016Course material created by D. Woit 13 /*Source: copy.c Purpose: copy file f1 to file f2 Usage: copy f1 f2 */ #include #define GOOD 0 #define BAD 1 int main (int argc, char *argv[]) { FILE *f1, *f2; int ch; if (argc != 3) { fprintf(stderr, "Usage: %s \n",argv[0]); exit(BAD); }

6/9/2016Course material created by D. Woit 14 if ((f1=fopen(argv[1],"r"))==NULL) { fprintf(stderr, "Cannot open %s\n",argv[1]); exit(BAD); } if ((f2=fopen(argv[2],"w"))==NULL) { fprintf(stderr, "Cannot open %s\n",argv[2]); exit(BAD); } while ((ch=fgetc(f1)) != EOF) fputc(ch,f2); fclose(f1); fclose(f2); exit(GOOD); }

6/9/2016Course material created by D. Woit 15 file i/o fgetc() returns EOF if 1) error in reading 2) hits EndOfFile can test for these separately feof(fp) non-0 if at EOF 0 otherwise ferror(fp) non-0 if error reading file 0 otherwise while (!feof(f1)) { ch=fgetc(f1); if (ferror(f1)) { fprintf(stderr, "Error reading... exit(BAD); } if (!feof(f1)) fputc(ch,f2); if (ferror(f2)) { fprintf(stderr, "Error writing... exit(BAD); }

6/9/2016Course material created by D. Woit 16 fgets(str, length, fp); gets chars from FILE fp and stores them in array str, until 1. '\n' read (and transfered to s) 2. (length-1) chars have been read, or 3. EOF returns ptr to str if successful NULL ptr otws Note: -fp could be stdin -the file read pointer advanced "length-1" chars in the file. e.g., fgets(X,3,f1); fgets(Y,3,f1); for file with abcde will put "12" in X and "34" in Y fputs(str,fp) writes str to "file" ptd to by fp returns EOF if error; positive int otws

6/9/2016Course material created by D. Woit 17 HMWK 1. Rewrite copy.c using fgets, fputs, feof and ferror assuming max line length in file is 128 chars. HMWK: 1. Write a program named prt.c that reads text from stdin until EOF and prints the number of lines and/or characters that were read in. The program takes one command line argument, which is l or c or b. If the argument is l, the program prints the number of lines, if c, the number of characters, and if b, it prints the number of both lines and chars.

6/9/2016Course material created by D. Woit 18 HMWK 2. Re-write program prt.c above except this time, the program takes 2 arguments, the second argument being the name of a file from which to read the text. Perform *full* error checking. 3. Re-write the above prt.c so that any number of files are processed (number of chars/lines printed for EACH, in order processed.) 4. Use fscanf and fprintf to read a file with 2 columns of integers, such as: and write the sum of each line to another file, e.g, 6 16 The file names are given on the command line

6/9/2016Course material created by D. Woit 19 perror You could also use function perror (print error) instead of fprintf(stderr...); When any system or library function is called *and fails*, its return code (integer) is put in a system variable that perror can access. (clobbered with each failure). perror translates the integer to an (human understandable) phrase and prints on stderr, prefixed by its string argument e.g., FILE *fp; if ( (fp = fopen("myfile","r")) == NULL ) { perror("fopen"); exit(1); }

6/9/2016Course material created by D. Woit 20 perror if "myfile" did not exist, stderr gets: fopen: No such file or directory (most of the built-in C functions use perror) FYI: All the error codes are defined in /usr/include/asm- generic/errno.h This C function perror in section 3 of man pages (man 3 perror)

6/9/2016Course material created by D. Woit 21 Structures Just as we can group items of same type into arrays, We can group items of dissimilar types into: structures struct s-name { type item1; type item2;... type itemN; } ;

6/9/2016Course material created by D. Woit 22 Structures e.g., a struct to describe cars (in struct1.c) struct car { char make[40]; char model[40]; unsigned int year; float price; } ; Then we can declare various variables of type struct car. struct car woit, chan1, chan2; //3 cars

6/9/2016Course material created by D. Woit 23 Assign woit's car: strcpy(woit.make, "Ferrari"); strcpy(woit.model, "F149"); woit.year = 2012; woit.price = ; Read in chan1's car: scanf("%s", chan1.make); //Porsche gets(chan1.model); //Carrera scanf("%u %f", &chan1.year, &chan1.price); // Print woit's car's make: printf("%s",woit.make); //prints Ferrari printf("%c",woit.make[4]); //prints what?

6/9/2016Course material created by D. Woit 24 Typedefs give your own name to any data type typedef short int Sint; int i; Sint j,k;

6/9/2016Course material created by D. Woit 25 Typedefs for structures struct car { char make[40]; char model[40]; unsigned int year; float price; } chan1 ; //chan1 is a variable like woit and chan2 struct car woit; struct car chan2; typedef struct { char make[40]; char model[40]; unsigned int year; float price; } car; //car is a new datatype (such as Sint above) car woit; car chan1, chan2;

6/9/2016Course material created by D. Woit 26 Arrays of structures car (struct car) is now a datatype, therefore, we can create an array of cars struct car chan[4]; /*if no typedef used*/ or car chan[4]; /*if typedef used*/ How do we use arrays of structures? chan's 0th car: chan[0].year = 1932; chan's 3rd car: chan[3].price = ; sizeof(struct car); /*no typedef*/ or sizeof(car); /*typedef*/ returns?

6/9/2016Course material created by D. Woit 27 HMWK: Write a program that reads an input file such as: Each line of the file contains a "complex number". Assume at most MAX=100 numbers are given. The program must create a structure for a complex number, and then store all the complex numbers in an array. (You must have an array of structures.) Then your program should loop through the array from end to front, and print out the complex numbers in it. E.g., your output should look like 8 + 2i i i 1 + 5i on stdout.