Blog

CSCB09 Software Tools and Systems Programming C – I/O Nandita Vijaykumar/Marcelo Ponce Winter 2022 Department of Computer and Mathematical Sciences – UTSC Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 1 / 17 C Programming Language Widely used and important. Impressive for a language that was invented in 1972! We will use the standard c99. Used in a huge range of disciplines, from OS, controlers, upto applications in scientific disciplines. https://www.tiobe.com/tiobe-index/ Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 2 / 17 Why C What do you think about C so far … Disappointed about the lack of support for strings, arrays, etc…. Turns out you also have to do much of memory management manually …. Your ride with Python Cruise control Seat heating Cup holders Automatic transmission Your ride with C Performance and speed But… no amenities… ( !) and it only comes with a stickshift… … compiled language Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 3 / 17 Why C What do you think about C so far … Disappointed about the lack of support for strings, arrays, etc…. Turns out you also have to do much of memory management manually …. Your ride with Python Cruise control Seat heating Cup holders Automatic transmission Your ride with C Performance and speed But… no amenities… ( !) and it only comes with a stickshift… …
compiled languageNandita Vijaykumar/Marcelo Ponce CSCB09 Software Tools
& Systems Programming – Week 02: C & I/OCMS/UTS – Winter 2022 3
/ 17 I/O I/O between User and Program From A48, output to terminal (STDOUT): printf() STDOUT, STDERR, STDIN What about input from keyboard Command line input STDIN input Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 4 / 17 Exercise 1 Implement a simplified version of the wc (word count) utility with only one functionality: Your program will use scanf to count the number of words (strings) the user inputs and print the count to the screen. The user signals the end of input (EOF = End of File) by hitting Ctrl-D (Ctrl-Z on Windows) on a new line (For simplicity you may assume no input word is longer than 20 characters) #include int main() { // YOUR CODE HERE !!! } Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 5 / 17 Exercise 1 – solution 1 #include 2 3 int main(){ 4 char input_string [20]; 5 int counter = 0; 6 7 while (scanf(“%s”, input_string) != EOF) { 8 counter = counter + 1; 9 } 10 11 printf(“%dn”, counter); 12 } Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 6 / 17 CLA: Command Line Arguments Command Line Arguments int main(int argc, char **argv) What is: char **arg Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 7 / 17 Quick review of string and array facts What is a string Array of chars Null character (’’) denotes the string end C library functions to operate on strings, char name [20]; strncpy(name , “CSCB09”, 20); // NOT: name = “CSCB09 “; What is the type of name → char* How would you declare an array of 30 strings char name_list [30]; name_list [0] = name; What is the type of name_list → char** Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 8 / 17 Quick review of string and array facts What is a string Array of chars Null character (’’) denotes the string end C library functions to operate on strings, char name [20]; strncpy(name , “CSCB09”, 20); // NOT: name = “CSCB09 “; What is the type of name → char* How would you declare an array of 30 strings char name_list [30]; name_list [0] = name; What is the type of name_list → char** Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 8 / 17 Quick review of string and array facts What is a string Array of chars Null character (’’) denotes the string end C library functions to operate on strings, char name [20]; strncpy(name , “CSCB09”, 20); // NOT: name = “CSCB09 “; What is the type of name → char* How would you declare an array of 30 strings char name_list [30]; name_list [0] = name; What is the type of name_list → char** Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 8 / 17 Quick review of string and array facts What is a string Array of chars Null character (’’) denotes the string end C library functions to operate on strings, char name [20]; strncpy(name , “CSCB09”, 20); // NOT: name = “CSCB09 “; What is the type of name → char* How would you declare an array of 30 strings char name_list [30]; name_list [0] = name; What is the type of name_list → char** Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 8 / 17 Quick review of string and array facts What is a string Array of chars Null character (’’) denotes the string end C library functions to operate on strings, char name [20]; strncpy(name , “CSCB09”, 20); // NOT: name = “CSCB09 “; What is the type of name → char* How would you declare an array of 30 strings char name_list [30]; name_list [0] = name; What is the type of name_list → char** Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 8 / 17 Quick review of string and array facts What is a string Array of chars Null character (’’) denotes the string end C library functions to operate on strings, char name [20]; strncpy(name , “CSCB09”, 20); // NOT: name = “CSCB09 “; What is the type of name → char* How would you declare an array of 30 strings char name_list [30]; name_list [0] = name; What is the type of name_list → char** Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 8 / 17 Quick review of string and array facts What is a string Array of chars Null character (’’) denotes the string end C library functions to operate on strings, char name [20]; strncpy(name , “CSCB09”, 20); // NOT: name = “CSCB09 “; What is the type of name → char* How would you declare an array of 30 strings char name_list [30]; name_list [0] = name; What is the type of name_list → char** Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 8 / 17 Command Line Arguments int main(int argc, char **argv) What is: char **arg An array of strings Need argc to know how many strings to expect in array. argv[1] is the first command line argument and so, what is argv[0] then Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 9 / 17 Command Line Arguments int main(int argc, char **argv) What is: char **arg An array of strings Need argc to know how many strings to expect in array. argv[1] is the first command line argument and so, what is argv[0] then Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 9 / 17 Exercise 2 Adding CLAs to wc… Extend your word count program to take exactly one command line argument. If the commandline argument is “-w” your program will print the number of words in user input (as before) If the commandline argument is “-c” your program will print the number of characters in user input As before, the user signals the end of input (EOF = End of File) by hitting Ctrl-D (Ctrl-Z on Windows) on a new line (For simplicity you may assume that the user does provide exactly one command line argument). Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 10 / 17 Exercise 2 – solution #include // basic IO, eg. printf #include // for strings manipulation int main(int argc , char argv) { char input_string [20]; char input_c; int counter = 0; // CLA processing: w _ words if (strcmp(argv[1], ” w”) == 0) { while (scanf(“%s”, input_string) != EOF) { counter = counter + 1; // increment counter } printf(“%d n”, counter); return 0; } 1 #include // basic IO, eg. printf 2 #include // for strings manipulation 3 4 int main(int argc , char argv) { 5 6 char input_string [20]; 7 char input_c; 8 int counter = 0; 9 10 // CLA processing: w _ words 11 if (strcmp(argv[1], ” w”) == 0) { 12 while (scanf(“%s”, input_string) != EOF) { 13 counter = counter + 1; // increment counter 14 } 15 printf(“%d n”, counter); 16 return 0; 17 } 18 19 // CLA processing: c _ characters 20 if (strcmp(argv[1], ” c”) == 0) { 21 while (scanf(“%c”, &input_c) != EOF) { 22 counter = counter + 1; // increment counter 23 } 24 printf(“%d n”, counter); 25 return 0; 26 } 27 28 printf(“Invalid argument!”); 29 } 1. In real program: check that argc==2 2. In real program: read at most 20 chars scanf(“%20s”, …) 3. Improvements: … Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 11 / 17 Exercise 2 – solution #include // basic IO, eg. printf #include // for strings manipulation int main(int argc , char argv) { char input_string [20]; char input_c; int counter = 0; // CLA processing: w _ words if (strcmp(argv[1], ” w”) == 0) { while (scanf(“%s”, input_string) != EOF) { counter = counter + 1; // increment counter } printf(“%d n”, counter); return 0; } 1 #include // basic IO, eg. printf 2 #include // for strings manipulation 3 4 int main(int argc , char argv) { 5 6 char inpu _string [20]; 7 char input_c; 8 int counter = 0; 9 10 // CLA rocess : w _ words 11 if (strcmp(argv[1], ” w”) == 0) { 12 while (scanf(“%s”, input_string) != EOF) { 13 counter = counter + 1; // increment counter 14 } 15 printf(“%d n”, counter); 16 return 0; 17 } 18 19 // CLA processing: c _ characters 20 if (st cmp(argv[1], ” c”) == 0) { 21 while (scanf(“%c”, &input_c) != EOF) { 22 counter = counter + 1; // increment counter 23 } 24 printf(“%d n”, counter); 25 return 0; 26 } 27 28 printf(“Invalid argument!”); 29 } 1. In real program: check that argc==2 2. In real program: read at most 20 chars scanf(“%20s”, …) 3. Improvements: … Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 11 / 17 I/O between user and program From A48, output to terminal (STDOUT): printf() What about input from terminal Command line input STDIN input What about file I/O Turns out you were doing file I/O already with printf & scanf int printf(const char *format, …) // writes to STDOUT int scanf(const char *format, …) // Reads from STDIN For general file I/O need to specify where to read to / write from: int fprintf(FILE *stream, const char *format, …) int fscanf(FILE *stream, const char *format, …) Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 12 / 17 I/O between user and program From A48, output to terminal (STDOUT): printf() What about input from terminal Command line input STDIN input What about file I/O Turns out you were doing file I/O already with printf & scanf int printf(const char *format, …) // writes to STDOUT int scanf(const char *format, …) // Reads from STDIN For general file I/O need to specify where to read to / write from: int fprintf(FILE *stream, const char *format, …) int fscanf(FILE *stream, const char *format, …) Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 12 / 17 I/O between user and program From A48, output to terminal (STDOUT): printf() What about input from terminal Command line input STDIN input What about file I/O Turns out you were doing file I/O already with printf & scanf int printf(const char *format, …) // writes to STDOUT int scanf(const char *format, …) // Reads from STDIN For general file I/O need to specify where to read to / write from: int fprintf(FILE *stream, const char *format, …) int fscanf(FILE *stream, const char *format, …) Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 12 / 17 I/O between user and program From A48, output to terminal (STDOUT): printf() What about input from terminal Command line input STDIN input What about file I/O Turns out you were doing file I/O already with printf & scanf int printf(const char *format, …) // writes to STDOUT int scanf(const char *format, …) // Reads from STDIN For general file I/O need to specify where to read to / write from: int fprintf(FILE *stream, const char *format, …) int fscanf(FILE *stream, const char *format, …) Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 12 / 17 I/O between user and program From A48, output to terminal (STDOUT): printf() What about input from terminal Command line input STDIN input What about file I/O Turns out you were doing file I/O already with printf & scanf int printf(const char *format, …) // writes to STDOUT int scanf(const char *format, …) // Reads from STDIN For general file I/O need to specify where to read to / write from: int fprintf(FILE *stream, const char *format, …) int fscanf(FILE *stream, const char *format, …) Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 12 / 17 I/O between user and program From A48, output to terminal (STDOUT): printf() What about input from terminal Command line input STDIN input What about file I/O Turns out you were doing file I/O already with printf & scanf int printf(const char *format, …) // writes to STDOUT int scanf(const char *format, …) // Reads from STDIN For general file I/O need to specify where to read to / write from: int fprintf(FILE *stream, const char *format, …) int fscanf(FILE *stream, const char *format, …) Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 12 / 17 File interfaces in C/Unix Two main mechanisms for managing open files: File descriptors (low-level, managed by OS): Each open file is identified by a small integer STDIN is 0, STDOUT is 1 Use for pipes, sockets (will see later what those are …) (Remember how I said in first lecture that everything is a file .. ) File pointers (aka streams, file handles) for regular files: A C language construct for easier working with file descriptors You use a pointer to a file structure (FILE *) as handle to a file. The file struct contains a file descriptor and a buffer. Use for regular files Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 13 / 17 File interfaces in C/Unix Two main mechanisms for managing open files: File descriptors (low-level, managed by OS): Each open file is identified by a small integer STDIN is 0, STDOUT is 1 Use for pipes, sockets (will see later what those are …) (Remember how I said in first lecture that everything is a file .. ) File pointers (aka streams, file handles) for regular files: A C language construct for easier working with file descriptors You use a pointer to a file structure (FILE *) as handle to a file. The file struct contains a file descriptor and a buffer. Use for regular files Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 13 / 17 File interfaces in C/Unix Two main mechanisms for managing open files: File descriptors (low-level, managed by OS): Each open file is identified by a small integer STDIN is 0, STDOUT is 1 Use for pipes, sockets (will see later what those are …) (Remember how I said in first lecture that everything is a file .. ) File pointers (aka streams, file handles) for regular files: A C language construct for easier working with file descriptors You use a pointer to a file structure (FILE *) as handle to a file. The file struct contains a file descriptor and a buffer. Use for regular files Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 13 / 17 Operating on regular files Let’s say we want to read from/write to a file my_file.txt For such, we need a file handle: FILE * A file first needs to be opened to obtain a FILE * FILE *fopen(const char *filename, const char *mode) filename identifies the file to open mode tells how to open the file: “r” for reading, “w” for writing, “a” for appending returns a pointer to a FILE struct which is the handle to the file. To close a file: void fclose(FILE *stream); FILE fp = fopen(“my_file.txt”, “w”); fprintf(fp, “Hello!n”); fclose(fp); Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 14 / 17 Operating on regular files Let’s say we want to read from/write to a file my_file.txt For such, we need a file handle: FILE * A file first needs to be opened to obtain a FILE * FILE *fopen(const char *filename, const char *mode) filename identifies the file to open mode tells how to open the file: “r” for reading, “w” for writing, “a” for appending returns a pointer to a FILE struct which is the handle to the file. To close a file: void fclose(FILE *stream); FILE fp = fopen(“my_file.txt”, “w”); fprintf(fp, “Hello!n”); fclose(fp); Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 14 / 17 Exercise 3 Extend our Exercise 1 word count program to take exactly one command line argument, which is a file name. This program will open the file, count the number of words in it and print the count. 1 #include 2 3 int main(){ 4 char input_string [20]; 5 int counter = 0; 6 7 while (scanf(“%s”, input_string) != EOF) { 8 counter = counter + 1; 9 } 10 11 printf(“%dn”, counter); 12 } FILE fopen(const char path , const char mode); int fscanf(FILE stream , const char format ,…); int fclose(FILE stream); Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 15 / 17 Exercise 3 Extend our Exercise 1 word count program to take exactly one command line argument, which is a file name. This program will open the file, count the number of words in it and print the count. 1 #include 2 3 int main(){ 4 char input_string [20]; 5 int counter = 0; 6 7 while (scanf(“%s”, input_string) != EOF) { 8 counter = counter + 1; 9 } 10 11 printf(“%dn”, counter); 12 } FILE fopen(const char path , const char mode); int fscanf(FILE stream , const char format ,…); int fclose(FILE stream); Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 15 / 17 Exercise 3 – solution #include int main(int argc , char argv){ char input_string [20]; int wc = 0; FILE input_file; input_file = fopen(argv[1], “r”); // In real programs , error check after opening file: // if (input_file == NULL) then there was an error while( fscanf(input_file , “%s”, input_string) != EOF) { wc = wc + 1; } fclose(input_file); printf(“%dn”, wc); } Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 16 / 17 Basic file I/O functions (stdio.h) FILE fopen(const char path , const char mode); int fscanf(FILE stream , const char format ,…); char fgets(char s, int size , FILE stream); char fgetc(FILE stream); int fprintf(FILE stream , const char format ,…) int fputs(const char str , FILE stream); int fseek(FILE stream , long int offset , int whence); void rewind(FILE stream); int fclose(FILE stream); Nandita
Vijaykumar/Marcelo Ponce CSCB09 Software Tools & Systems
Programming – Week 02: C & I/OCMS/UTS – Winter 2022 17 / 17