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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#include #define MAXLINE 1000void 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#include #include #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 \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; }
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