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Trying to read in from a file

Posted on 2003-11-28
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Last Modified: 2012-05-04
I need a simple way (command line program, if there is a way) to ask for a certain X number of bytes from a file and have it print out the first X characters to standard output.  It's for testing.

Scorpantula
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Question by:scorpantula
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5 Comments
 
LVL 44

Accepted Solution

by:
Karl Heinz Kremer earned 250 total points
ID: 9840079
#include <stdio.h>

int main(int argc, char * argv[])
{
    FILE * in;
    int limit;
    int i;

    if (argc != 3)
    {
        fprintf(stderr, "Usage: %s <filename> <byte count>\n", argv[0]);
        exit(-1);
    }

    in = fopen(argv[1], "r");
    if (in == NULL)
    {
        fprintf(stderr, "Cannot open file %s\n", argv[1]);
        exit(-2);
    }

    limit = atoi(argv[2]);

    for (i=0; i < limit; i++)
    {
        putchar(fgetc(in));
    }

    putchar('\n');
    fclose(in);
}

Save this to a file (e.g. test.c), then run "make test", which will create the executable test. Then run the command with two arguments on the command line: The first one is the file name, and the second one the number of characters.

e.g.:

./test test.c 45

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LVL 44

Expert Comment

by:Karl Heinz Kremer
ID: 9840089
Forgot to say this: The program woks for text files for binary files you need to change the output function, but this depends on what you want to see in the output. (e.g. hex dump, octal values, ...)
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LVL 5

Assisted Solution

by:mtmike
mtmike earned 250 total points
ID: 9840616
Use head (man head), eg

head -c X FILE

to print out the first X bytes of FILE.
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