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ETE 132 Lecture 8

ETE 132 Lecture 8. By Munirul Haque. Topics. I/O, Streams, Files. Files. The library stdio.h defines a structure called FILE . You don’t need to know any of the details of how a FILE works, you just need to know how to point to them. A pointer to a file is called a “file handle”.

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ETE 132 Lecture 8

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  1. ETE 132Lecture 8 By Munirul Haque

  2. Topics • I/O, Streams, Files

  3. Files • The library stdio.h defines a structure called FILE. • You don’t need to know any of the details of how a FILE works, you just need to know how to point to them. • A pointer to a file is called a “file handle”.

  4. Writing to a File void main() { FILE *fp; /* pointer to a file */ /* open WRITEME.txt for reading */ fp = fopen("WRITEME.txt", “w"); /* do stuff with the file */ fprintf(fp,"This goes in the file"); /* close the file -- it’s a good habit */ fclose(fp); }

  5. fopen • The function fopen accepts a string corresponding to the name of the filename, and another string the says whether we want to open the file to • read ("r"), • Write ("w"), or • append ("a"). • If there is any error, fopen returns the pointer value NULL.

  6. Printf and Scanf with Files • Up to now, we’ve been using printf to print messages (to “standard output”), and scanf to receive input from the keyboard (from “standard input”). • These can be generalized to the functions fprintf and fscanf, which write to and read from a particular file.

  7. Printf and Scanf with Files • Given a file pointer fp, the statement: • fprintf(fp,"This goes in the file"); writes to the file handled by fp. • The statement: fscanf(fp,"%d",&intvar); reads an integer from the file.

  8. Other ways to read and write • There are more rudimentary ways to read from files and write to files. • Suppose that fp is a file pointer. • The function getc(fp) returns a single character read from the file. putc(c,fp); • writes the character c to the file.

  9. End of File • feof() returns non-zero if fp reaches end-of-file, otherwise zero. FILE *fp; while(!feof(fp)) ch = getc(ch);

  10. Reading from file • Reading character by character File *fp; char ch; fp = fopen(“myfile”, “r”); // open file to read while(!feof(fp)) { // read until end-of-file ch = getc(fp); printf(“%c”,ch); } fclose(fp); // close the file stream

  11. Writing to file • Writing character by character File *fp; char ch; fp = fopen(“myfile”, “w”); // open file to write while(1) { scanf(“%c”, &ch); if (ch == ‘\n’) break; // read until newline found putc(ch, fp); } fclose(fp);

  12. Copy file FILE *from, *to; char ch; from = fopen(“input.txt”, “r”); to = fopen(“output.txt”, “w”); while (!feof(from)) { ch = getc(from); putc (ch, to); } fclose(from); fclose(to);

  13. fscanf() • Read from file to specific variables double d; int i; char str[20], ch; FILE *fp; fscanf(fp, “%lf %d %s %c”, &d, &i, str, &ch); printf(“%lf %d %s %c”, d, i, str, c); fclose(fp);

  14. fprintf() • Write values from variables to file double d = 1234.5; int i = 10; char str[20] = “Hello”, ch = ‘Q’; FILE *fp; fprintf(fp, “%lf %d %s %c”, d, i, str, c); fclose(fp);

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