1. 1 TDBA66, vt-04, Lecture Ch9 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 It has two lines  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

2. 2 TDBA66, vt-04, Lecture Ch9 EOF EOF is defined in 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);

3. 3 TDBA66, vt-04, Lecture Ch9 Using text files 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); }

4. 4 TDBA66, vt-04, Lecture Ch9 /* 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 #define STRSIZ 80 int main(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> "); }

5. 5 TDBA66, vt-04, Lecture Ch9 /*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); }

6. 6 TDBA66, vt-04, Lecture Ch9 Binary files Binary files can not be created by an editor (as with text files) A binary file is created by writing on it from a C-program If a human should not read the file it saves time and memory to use binary files The internal representation in bits ia written to a binary file Contents of databases are typically binary

7. 7 TDBA66, vt-04, Lecture Ch9 Example Figure 10.3 (extended) Creating a Binary File of Integers and read them into a vector of integers FILE *binaryp, *inbinp; int i, list[255]; binaryp = fopen("nums.bin", "wb"); for (i = 2; i <= 500; i += 2) fwrite(&i, sizeof (int), 1, binaryp); fclose(binaryp); /* read 250 integers into a vector */ inbinp = fopen(”nums.bin”,”rb”); fread(list, sizeof(int), 250, inbinp); fclose(inbinp); …………

8. 8 TDBA66, vt-04, Lecture Ch9 Figure 10.4 Outline and Function main for Metals Database Inquiry Program /* * Displays all metals in the database that satisfy the search * parameters specified by the program user. */ #include #include #define MAX_DENSITY 20.0 /*maximum density (g/cm^3)*/ #define MAX_MELT_PT 4000 /*maximum melting point(deg.C)*/ #define MAX_TENS_MOD 350 /*maximum tensile modulus(GPa)*/ #define MAX_DAYS 90 /* maximum days to delivery */ #define STR_SIZ 80 /* number of characters in string*/ typedef struct { /* metal structure type */ char name[STR_SIZ]; double density; /* g/cm^3 */ int melt_pt, /* melting point in degrees C */ tens_mod, /* tensile modulus in GPa */ days_to_deliv; /* days from order to delivery */ } metal_t; typedef struct { /* search parameter bounds type */ char low_name[STR_SIZ], high_name[STR_SIZ]; double low_density, high_density; int low_melt_pt, high_melt_pt, low_tens_mod, high_tens_mod, low_days, high_days; } search_params_t;

9. 9 TDBA66, vt-04, Lecture Ch9 Fig. 10.4 cont. /* Insert prototypes of other functions needed.*/ /* * Prompts the user to enter the search parameters. */ search_params_t get_params(void); /* * Displays records of all metals in the inventory that satisfy search parameters. */ void display_match(FILE *databasep, /* input - file pointer to binary database file*/ search_params_t params);/* input - search parameter bounds*/ int main(void){ char inv_filename[STR_SIZ]; /*name of inventory file */ FILE *inventoryp; /* inventory file pointer*/ search_params_t params; /* search parameter bounds */ /* Get name of inventory file and open it*/ printf("Enter name of inventory file> "); scanf("%s", inv_filename); fflush(stdin); inventoryp = fopen(inv_filename, "rb"); /* Get the search parameters */ params = get_params(); /*Display all metals that satisfy the search parameters */ display_match(inventoryp, params); return(0); }