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S09: I/O

Required: PM: Ch 11, pgs 205-243

Recommended: K&R, Chapter 7Data Input and Output

BYU CS 224 Input and Output 2

CS 224Chapter Project Homework

S00: IntroductionUnit 1: Digital Logic

S01: Data TypesS02: Digital Logic

L01: Warm-upL02: FSM

HW01HW02

Unit 2: ISAS03: ISAS04: MicroarchitectureS05: Stacks / InterruptsS06: Assembly

L03: BlinkyL04: MicroarchL05b: Traffic LightL06a: Morse Code

HW03HW04HW05HW06

Unit 3: CS07: C LanguageS08: PointersS09: StructsS10: I/O

L07b: Morse IIL08a: LifeL09b: Snake

HW07HW08HW09HW10

Input and Output 3BYU CS 224

Learning Outcomes… Students will be able to:

Find and use standard C functions.

Interpret a data stream according to a specified format.

Direct character output to a data stream.

Assign a data stream to an I/O device, file, or memory.


Topics… Standard Libraries Input/Output Data Streams printf() scanf() File I/O fprintf and fscanf sprintf and sscanf

Quiz 10.1

BYU CS 224 Input and Output 5

2. Name 5 ways to improve your skills as a programmer

1. What makes one person’s code better/worse than another?


C Standard Library Standard libraries promote cross-platform

compatibility. Useful for building complex programs. Functions, types, and macros of the standard

library are accessed by the #include directive. Headers may be included in any order (and any

number of times). Actual I/O libraries can be linked statically or

dynamically.

Standard Libraries


ANSI Standard Libraries <assert.h> Diagnostics <ctype.h> Character Class Tests <errno.h> Error Codes Reported by (Some) Library

Functions <float.h> Implementation-defined Floating-Point Limits <limits.h> Implementation-defined Limits <locale.h> Locale-specific Information <math.h> Mathematical Functions <setjmp.h> Non-local Jumps <signal.h> Signals <stdarg.h> Variable Argument Lists <stddef.h> Definitions of General Use <stdio.h> Input and Output <stdlib.h> Utility functions <string.h> String functions <time.h> Time and Date functions

Standard Libraries


<string.h> Copy one string into another

char* strcpy (const char* dest, const char* src); char* strncpy (const char* string1, const char* string2, size_t n)

Compare string1 and string2 to determine alphabetic order int strcmp (const char* string1,const char* string2); int strncmp (const char* string1, char* string2, size_t n);

Determine the length of a string int strlen (const char* string);

Append characters from string2 to string1 char* strcat (const char* string1, const char* string2); char* strncat (const char* string1, const char* string2, size_t n);

Find a string in a string char* strstr (char* string1, const char* string2);

String Library

Input and Output 9

<string.h> memchr memcmp memcpy memmove memset

strchr strcoll strcspn strerror strpbrk strrchr strspn strtok strxfrm

BYU CS 224

String Library

Input and Output 10

<stdlib.h> String conversion

atof Convert string to double atoi Convert string to integer atol Convert string to long integer atoll Convert string to long long integer strtod Convert string to double strtof Convert string to float strtol Convert string to long integer strtold Convert string to long double strtoll Convert string to long long integer strtoul Convert string to unsigned long integer strtoullConvert string to unsigned long long integer

BYU CS 224

Standard General Utilities Library

Input and Output 11

<stdlib.h> Pseudo-random sequence generation

rand Generate random number srand Initialize random number generator

Dynamic memory management calloc Allocate and zero-initialize array free Deallocate memory block malloc Allocate memory block realloc Reallocate memory block

Searching and sorting bsearch Binary search in array qsort Sort elements of array

BYU CS 224


Input and Output 12

<stdlib.h> Integer arithmethics

abs Absolute value div Integral division labs Absolute value ldiv Integral division llabs Absolute value lldiv Integral division

Types div_t Structure returned by div (type ) ldiv_t Structure returned by ldiv (type ) lldiv_t Structure returned by lldiv (type ) size_t Unsigned integral type (type )

BYU CS 224


Input and Output 13

Quiz 10.2

1. In which standard library would I find the following?

a) absb) malloc / freec) memcpy / memsetd) printf / putchar

2. What is an I/O Stream?

BYU CS 224


I/O Data Streams I/O is not directly supported by C but by a set of standard

library functions defined by the ANSI C standard. The stdio.h header file contains function declarations for I/O and

preprocessor macros related to I/O. stdio.h does not contain the source code for I/O library functions!

All C character based I/O is performed on streams. All I/O streams must be opened and closed A sequence of characters received from the keyboard is an

example of a text stream In standard C there are 3 streams automatically opened

upon program execution: stdin is the input stream stdout is the output stream stderr stream for error messages

Data Streams


Formatted Output The printf function outputs formatted values to

the stdout stream using putcprintf( const char *format, ... );

The format string contains two object types: Ordinary characters that are copied to the output

stream Conversion specifications which cause conversion

and printing of the next argument in the argument list.printf("\nX = %d, Y = %d", x, y);

printf()

Conversionspecifications Characters


Format Options The format specifier uses the format:

%[flags][width][.precision][length]specifier Formatting options are inserted between the %

and the conversion character: Field width "%4d" Length modifier "%ld" Left justified "%-4d" Zero padded "%04d" Sign "%+4d" Variable field width "%*d" Characters "\a", "\b", "\n", "\r", "\t", "\v", "\xnn"

printf()

Specifiers:Decimal %d or %iString %sCharacter %cHexadecimal %xUnsigned decimal %uFloating point %fScientific notation %eHex floating point %aPointer %p% %%


Formatted Output A period separates the field width from the precision

when formatting floating point numbers:printf("Speed = %10.2f", speed);

A variable field width is specified using an asterisk (*) formatting option along with a length argument (which must be an int):

printf("%*s", max, s); Left justification is specified by a minus

character (-). The plus character (+) isreplaced by the sign (either “+” or “-”). A space (' ') is replace by “-” if negative.

printf("%-+04d", 10);

printf()

\a bell (alert)

\n newline

\r return

\t tab

\b backspace

\\ backslash

\' single quote

\" double quote

\0nnn ASCII code – oct

\xnnn ASCII code – hex


Formatted Output Examples

int a = 100;int b = 65;char c = 'z';char banner[ ] = "Hola!";double pi = 3.14159;

printf("The variable 'a' decimal: %d\n", a);printf("The variable 'a' hex: %x\n", a);printf("'a' plus 'b' as character: %c\n", a+b);printf("A char %c.\t A string %s\n A float %7.4f\n", c, banner, pi);

printf()

Decimal %d or %iString %sCharacter %cHexadecimal %xUnsigned decimal %uFloating point %fScientific notation %ePointer %p% %%


Full Formatted Output Enableprintf()


Formatted Input The function scanf is similar to printf, providing

many of the same conversion facilities in the opposite direction:

scanf( const char *format, ... ); reads characters from the standard input (stdin), interprets them according to the specification in format, stores the results through the remaining arguments.

The format argument is a string; all other arguments must be a pointers indicating where the corresponding converted input should be stored.

scanf()


scanf Conversion For each data conversion, scanf will skip whitespace

characters and then read ASCII characters until it encounters the first character that should NOT be included in the converted value.

%d Reads until first non-digit.%x Reads until first non-digit (in hex).%s Reads until first whitespace character.

Literals in format string must match literals in theinput stream.

Data arguments must be pointers, because scanfstores the converted value to that memory address.

scanf()


scanf Return Value The scanf function returns an integer, which indicates

the number of successful conversions performed. This lets the program check whether the input stream

was in the proper format. Example:

scanf("%s %d/%d/%d %lf", name, &bMonth, &bDay, &bYear, &gpa);

Input Stream Return ValueMudd 02/16/69 3.02 5

Muss 02 16 69 3.02 2

Doesn't match literal '/', so scanf quitsafter second conversion.

scanf()


Quiz 10.3 What will the following do?

1. Output of the programto the right?

2. int n = 0;scanf("%d", n);

3. scanf("%d");

4. printf("\nValue=%d");

#include <stdio.h>

int main(void){ const char text[] = "Hello world"; int i; for ( i = 1; i < 12; ++i ) { printf("\"%*s\"\n", i, text); }}


I/O from Files General-purpose I/O functions allow us to specify the

stream on which they act Must declare a pointer to a FILE struct for each

physical file we want to manipulateFILE* infile;FILE* outfile;

The I/O stream is "opened" and the FILE struct instantiated by the fopen function

Arguments include the name of file to open and a description of the operation modes we want to perform on that file

infile = fopen("myinfile", "r");outfile = fopen("myoutfile", "w");

Returns pointer to file descriptor or NULL if unsuccessful

File I/O


I/O from Files File operation modes are:

"r" for reading "w" for writing (an existing file will lose its contents) "a" for appending "r+" for reading and writing "b" for binary data

Once a file is opened, it can be read from or written to with functions such as

fgetc Read character from stream fputc Write character to stream fread Read block of data from stream fwrite Write block of data to stream fseek Reposition stream position indicator fscanf Read formatted data from stream fprintf Write formatted output to stream

File I/O


I/O from Files#define LIMIT 1000int main(){ FILE* infile; FILE* outfile; double prices[LIMIT]; int i=0;

infile = fopen("myinputfile", "r"); // open for reading outfile = fopen("myoutputfile", "w"); // open for writting if ((infile != NULL) && (outfile != NULL)) { while (i < LIMIT) { if ((fscanf(infile, "%lf", &prices[i]) == EOF)) break; printf("\nprice[%d] = %10.2lf", i, prices[i]); // ... process prices[i] i += 1; } } else printf("\nfopen unsuccessful!"); fclose(infile); fclose(outfile);}

File I/O


Quiz 10.4 Write an ASCII to integer function (ascii to integer).

1. Account for leading spaces and negative numbers.2. Stop conversion at any non-digit.3. Use a ternary operator somewhere in your implementation

Prototype:int my_atoi(char* s);

Exampleprintf("-345 = %d", my_atoi(" -345"));


sprintf and sscanf sprintf converts binary numbers to a string

int sprintf(char* buffer, const char* fmt,…); buffer – char array big enough to hold converted number(s) fmt – format specification Variable list to be converted Returns number of characters in converted string (not including null

character Useful in converting data to strings

sscanf converts a string to binary numbers int sscanf(char* buffer, const char* fmt,…);

buffer – char array contains data to be converted fmt – format specification List of pointers to variables to hold converted values Returns number of items converted

Useful to convert character data files

sprintf / sscanf

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t ncompare string1