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Text files

Text files. Text file contains ASCII-characters New line and end-of-file are special characters in a text file Ex. 1 This is a text<newline>It has two lines<newline><end-of-file> Examples of predifined text files stdin, stdout, stderr (these are file pointers)

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Text files

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  1. Text files • Text file contains ASCII-characters • New line and end-of-file are special characters in a text file Ex. 1 • This is a text<newline>It has two lines<newline><end-of-file> • Examples of predifined text files stdin, stdout, stderr (these are file pointers) • stderr always associated with the screen • stdin, stdout might be re-directed to other text files TDBA66, vt-04, Lecture Ch9

  2. EOF EOF is defined in <stdio.h> and is returned from scanf() or fscanf() if end-of-file of the read file is detected Possible to check if EOF is read by e.g. for (status=scanf(”%d”, &num); status != EOF; status=scanf(”%d”, &num)) process(num); e.g. while (fscanf(infpt,”%d”, &num) != EOF) process(num); TDBA66, vt-04, Lecture Ch9

  3. Declare file pointers • Open a file for reading or writing • -check if opening was ok • Use it/them • Close them before ending program • Ex. 1 • FILE *inf, *outf; • if ((inf=fopen(”filname1.txt”,”r”)) == NULL){ • fprintf(stderr,”Error when opening filname1.txt”); • exit(-1); • } • if ((outf=fopen(”filname2.txt”,”w”))== NULL){ • fprintf(stderr,”Error when opening filname2.txt”); • exit(-2); • } Using text files TDBA66, vt-04, Lecture Ch9

  4. /* Makes a backup file. Repeatedly prompts for the name of a file to * back up until a name is provided that corresponds to an available * file. Then it prompts for the name of the backup file and creates * the file copy. */ #include <stdio.h> #define STRSIZ 80 intmain(void){ char in_name[STRSIZ], /* strings giving names */ out_name[STRSIZ]; /* of input and backup files */ FILE *inp, /* file pointers for input and */ *outp; /* backup files */ char ch; /* one character of input file */ int status; /* status of input operation */ /* Get the name of the file to back up and open the file for input*/ printf("Enter name of file you want to back up> "); for (scanf("%s", in_name); (inp = fopen(in_name, "r")) == NULL; scanf("%s", in_name)) { printf("Cannot open %s for input\n", in_name); printf("Re-enter file name> "); } TDBA66, vt-04, Lecture Ch9

  5. /*Get name to use for backup file and open file for output */ printf("Enter name for backup copy> "); for (scanf("%s", out_name); (outp = fopen(out_name, "w")) == NULL; scanf("%s", out_name)) { printf("Cannot open %s for output\n", out_name); printf("Re-enter file name> "); } /* Make backup copy one character at a time */ for (status = fscanf(inp, "%c", &ch); status != EOF; status = fscanf(inp, "%c", &ch)) fprintf(outp, "%c", ch); /* Close files and notify user of backup completion */ fclose(inp); fclose(outp); printf("Copied %s to %s.\n", in_name, out_name); return(0); } TDBA66, vt-04, Lecture Ch9

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