Writing to Files
Data can be written to the file using fputc and fprintf. The following example uses the fgetc and fputc functions to make a copy of a text file.
#include <stdio.h>
int main()
{
FILE *in, *out;
int key;
if ((in = fopen("tarun.txt", "r")) == NULL)
{
puts("Unable to open the file");
return 0;
}
out = fopen("copy.txt", "w");
while (!feof(in))
{
key = fgetc(in);
if (!feof(in))
fputc(key, out);
}
fclose(in);
fclose(out);
return 0;
}
The fprintf function can be used to write formatted data to a file.
fprintf(out, "Date: %02d/%02d/%02d\n",
day, month, year);
Command Line Arguments with C
The ANSI C definition for declaring the main( ) function is either:
int main() or int main(int argc, char **argv)
The second version allows arguments to be passed from the command line. The parameter argc is an argument counter and contains the number of parameters passed from the command line. The parameter argv is the argument vector which is an array of pointers to strings that represent the actual parameters passed.
The following example allows any number of arguments to be passed from the command line and prints them out. argv[0] is the actual program. The program must be run from a command prompt.
#include <stdio.h>
int main(int argc, char **argv)
{
int counter;
puts("The arguments to the program are:");
for (counter=0; counter<argc; counter++)
puts(argv[counter]);
return 0;
}
If the program name was count.c, it could be called as follows from the command line.
count 3
or
count 7
or
count 192 etc.
The next example uses the file handling routines to copy a text file to a new file. For example the command line argument could be called as:
txtcpy one.txt two.txt
#include <stdio.h>
int main(int argc, char **argv)
{
FILE *in, *out;
int key;
if (argc < 3)
{
puts("Usage: txtcpy source destination\n");
puts("The source must be an existing file");
puts("If the destination file exists, it will be
overwritten");
return 0;
}
if ((in = fopen(argv[1], "r")) == NULL)
{
puts("Unable to open the file to be copied");
return 0;
}
if ((out = fopen(argv[2], "w")) == NULL)
{
puts("Unable to open the output file");
return 0;
}
while (!feof(in))
{
key = fgetc(in);
if (!feof(in))
fputc(key, out);
}
fclose(in);
fclose(out);
return 0;
}
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