c程序设计语言_习题7-6_对比两个输入文本文件_输出它们不同的第一行_并且要记录行号

Write a program to compare two files, printing the first line where they differ.Here's Rick's solution:

/******************************************************
KnR 7-6
--------
Write a program to compare two files and print the
first line where they differ.

Author: Rick Dearman
email: rick@ricken.demon.co.uk

Note: This program prints ALL the lines that are
different using the <> indicators used by
the unix diff command. However this program
will not cope with something as simple as a
line being removed.

In reality the program would be more useful
if it searched forward for matching lines.
This would be a better indicator of the simple
removal of some lines.

This has lead me to track down a version of the
"diff" command available on GNU/Linux systems.
for more information go to the web site at:
www.gnu.org

******************************************************/

#include <stdio.h>
#include <string.h>
#define MAXLINE 1000

void diff_line( char *lineone, char *linetwo, int linenumber )
{
if(strcmp (lineone, linetwo) < 0 || strcmp (lineone, linetwo) > 0)
printf( "%d<%s\n%d>%s\n", linenumber, lineone, linenumber, linetwo);
}

int main(int argc, char *argv[] )
{
FILE *fp1, *fp2;
char fp1_line[MAXLINE], fp2_line[MAXLINE];
int i;

if ( argc != 3 )
{
printf("differ fileone filetwo\n");
exit(0);
}

fp1 = fopen( argv[1], "r" );
if ( ! fp1 )
{
printf("Error opening file %s\n", argv[1]);
}

fp2 = fopen( argv[2], "r" );
if ( ! fp2 )
{
printf("Error opening file %s\n", argv[2]);
}
i = 0;
while ( (fgets(fp1_line, MAXLINE, fp1) != NULL)
&& (fgets(fp2_line, MAXLINE, fp2) != NULL))
{
diff_line( fp1_line, fp2_line, i );
i++;
}

return 0;
}

and here's "flippant squirrel"'s solution:

/* Exercise 7-6 - write a program to compare two files, printing the first line
* where they differ
*
* Note : I amended this a bit...if a file is shorter than the other, but is identical
* up to that point, the program prints out "EOF" as the string that's not equal.
*
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define BUFF_SIZE 1000

/* uses fgets, removes the '\n' at the end of the string if it exists */
char *safegets(char *buffer, int length, FILE *file)
{
char *ptr;
int len;

if (buffer != NULL)
{
ptr = fgets(buffer, length, file);

if (ptr != NULL)
{
len = strlen(buffer);

if (len > 0)
{
if (buffer[len - 1] == '\n')
{
buffer[len - 1] = '\0';
}
}
}

return ptr;
}

return NULL;
}

int main(int argc, char *argv[])
{
FILE *leftFile, *rightFile;
char buff1[BUFF_SIZE], buff2[BUFF_SIZE];
char *ptr1, *ptr2;
unsigned long lineNum = 0;

if (argc < 3)
{
fprintf(stderr, "Usage : 7_6 <path to file> <path to file>\n");
return 0;
}

if (!(leftFile = fopen(argv[1], "r")))
{
fprintf(stderr, "Couldn't open %s for reading\n", argv[1]);
return 0;
}

if (!(rightFile = fopen(argv[2], "r")))
{
fprintf(stderr, "Couldn't open %s for reading\n", argv[2]);
fclose(leftFile); /* RJH 10 Jul 2000 */
return 0;
}

/* read through each file, line by line */
ptr1 = safegets(buff1, BUFF_SIZE, leftFile);
ptr2 = safegets(buff2, BUFF_SIZE, rightFile);
++lineNum;

/* stop when either we've exhausted either file's data */
while (ptr1 != NULL && ptr2 != NULL)
{
/* compare the two lines */
if (strcmp(buff1, buff2) != 0)
{
printf("Difference:\n");
printf("%lu\t\"%s\" != \"%s\"\n", lineNum, buff1, buff2);
goto CleanUp;
}

ptr1 = safegets(buff1, BUFF_SIZE, leftFile);
ptr2 = safegets(buff2, BUFF_SIZE, rightFile);
++lineNum;
}

/*
* if one of the files ended prematurely, it definitely
* isn't equivalent to the other
*/
if (ptr1 != NULL && ptr2 == NULL)
{
printf("Difference:\n");
printf("%lu\t\"%s\" != \"EOF\"\n", lineNum, buff1);
}
else if (ptr1 == NULL && ptr2 != NULL)
{
printf("Difference:\n");
printf("%lu\t\"EOF\" != \"%s\"\n", lineNum, buff2);
}
else
{
printf("No differences\n");
}

CleanUp:

fclose(leftFile);
fclose(rightFile);
return EXIT_SUCCESS;
}