C how to search string in a file?
I have a problem with my code, I'm trying to search a string in a file and I can read it but, when I compare two strings it takes only the last one of the file as equal to the the first string entered with the scanf()
.
So imagine I wrote in my file three words and each one is returning to the line.
test
test12
test123
If in my scanf()
I write test12
for example or test
when it's going to read it will return false to the compare so (!== 0). But if I write test123
it will works because it's the last word of the file but I don't know why?
char word[26];
char singleLine[26];
FILE *file = fopen("bin/Release/myWords.txt", "a+");
scanf("%26s", word);
if (file != NULL) {
while (!feof(file)) {
fgets(singleLine, 26, file);
compare = strcmp(singleLine, word);
if (compare == 0) {
printf("n%sn",word);
}
}
fclose(file);
}
c file string-comparison
add a comment |
I have a problem with my code, I'm trying to search a string in a file and I can read it but, when I compare two strings it takes only the last one of the file as equal to the the first string entered with the scanf()
.
So imagine I wrote in my file three words and each one is returning to the line.
test
test12
test123
If in my scanf()
I write test12
for example or test
when it's going to read it will return false to the compare so (!== 0). But if I write test123
it will works because it's the last word of the file but I don't know why?
char word[26];
char singleLine[26];
FILE *file = fopen("bin/Release/myWords.txt", "a+");
scanf("%26s", word);
if (file != NULL) {
while (!feof(file)) {
fgets(singleLine, 26, file);
compare = strcmp(singleLine, word);
if (compare == 0) {
printf("n%sn",word);
}
}
fclose(file);
}
c file string-comparison
1
see Why is “while ( !feof (file) )” always wrong?
– yano
Nov 20 '18 at 21:31
fgets
includes the final 'n`, so it gets compared along with the rest of your string.
– usr2564301
Nov 20 '18 at 21:35
you need to learn how to use the debugger and use it to see the strings being compared. Until you do this you will never be able to write code.
– john elemans
Nov 20 '18 at 21:46
add a comment |
I have a problem with my code, I'm trying to search a string in a file and I can read it but, when I compare two strings it takes only the last one of the file as equal to the the first string entered with the scanf()
.
So imagine I wrote in my file three words and each one is returning to the line.
test
test12
test123
If in my scanf()
I write test12
for example or test
when it's going to read it will return false to the compare so (!== 0). But if I write test123
it will works because it's the last word of the file but I don't know why?
char word[26];
char singleLine[26];
FILE *file = fopen("bin/Release/myWords.txt", "a+");
scanf("%26s", word);
if (file != NULL) {
while (!feof(file)) {
fgets(singleLine, 26, file);
compare = strcmp(singleLine, word);
if (compare == 0) {
printf("n%sn",word);
}
}
fclose(file);
}
c file string-comparison
I have a problem with my code, I'm trying to search a string in a file and I can read it but, when I compare two strings it takes only the last one of the file as equal to the the first string entered with the scanf()
.
So imagine I wrote in my file three words and each one is returning to the line.
test
test12
test123
If in my scanf()
I write test12
for example or test
when it's going to read it will return false to the compare so (!== 0). But if I write test123
it will works because it's the last word of the file but I don't know why?
char word[26];
char singleLine[26];
FILE *file = fopen("bin/Release/myWords.txt", "a+");
scanf("%26s", word);
if (file != NULL) {
while (!feof(file)) {
fgets(singleLine, 26, file);
compare = strcmp(singleLine, word);
if (compare == 0) {
printf("n%sn",word);
}
}
fclose(file);
}
c file string-comparison
c file string-comparison
edited Nov 20 '18 at 22:09
halfer
14.6k758113
14.6k758113
asked Nov 20 '18 at 21:27
Louis HervéLouis Hervé
153
153
1
see Why is “while ( !feof (file) )” always wrong?
– yano
Nov 20 '18 at 21:31
fgets
includes the final 'n`, so it gets compared along with the rest of your string.
– usr2564301
Nov 20 '18 at 21:35
you need to learn how to use the debugger and use it to see the strings being compared. Until you do this you will never be able to write code.
– john elemans
Nov 20 '18 at 21:46
add a comment |
1
see Why is “while ( !feof (file) )” always wrong?
– yano
Nov 20 '18 at 21:31
fgets
includes the final 'n`, so it gets compared along with the rest of your string.
– usr2564301
Nov 20 '18 at 21:35
you need to learn how to use the debugger and use it to see the strings being compared. Until you do this you will never be able to write code.
– john elemans
Nov 20 '18 at 21:46
1
1
see Why is “while ( !feof (file) )” always wrong?
– yano
Nov 20 '18 at 21:31
see Why is “while ( !feof (file) )” always wrong?
– yano
Nov 20 '18 at 21:31
fgets
includes the final 'n`, so it gets compared along with the rest of your string.– usr2564301
Nov 20 '18 at 21:35
fgets
includes the final 'n`, so it gets compared along with the rest of your string.– usr2564301
Nov 20 '18 at 21:35
you need to learn how to use the debugger and use it to see the strings being compared. Until you do this you will never be able to write code.
– john elemans
Nov 20 '18 at 21:46
you need to learn how to use the debugger and use it to see the strings being compared. Until you do this you will never be able to write code.
– john elemans
Nov 20 '18 at 21:46
add a comment |
1 Answer
1
active
oldest
votes
Your program only works in very special cases and has several problems:
scanf("%26s", word);
may affect up to 27 bytes in the destination array, which is defined with a length of only26
.- furthermore, you should check the return value to avoid undefined behavior on invalid input.
fopen("bin/Release/myWords.txt", "a+");
opens the file in append mode: is this necessary?
while (!feof(file))
is always wrong, you should instead check the return value offgets()
that returnsNULL
at end of file.
compare = strcmp(singleLine, word);
only compares for an exact math of the full line, which can only happen if the word has 25 characters, otherwise the trailing newline insingleLine
will cause the comparison to fail. Furthermore, broken lines may cause unexpected results, as well as if the file does not end with a newline.- the reason it matches the last word in the file is you forget to write a trailing newline after the last word in the file, so the last
fgets()
fills the buffer with the exact word and no trailing newline. - if you search for matches inside the line, you should use a larger buffer and search for a match with
strstr
. - if you search for a exact match, you should strip the trailing newline before the comparison.
Here is a modified version:
#include <stdio.h>
#include <string.h>
int main() {
char word[27];
char singleLine[256];
FILE *file = fopen("bin/Release/myWords.txt", "r");
if (scanf("%26s", word) != 1)
return 1;
if (file != NULL) {
while (fgets(singleLine, sizeof singleLine, file)) {
singleLine[strcspn(singleLine, "n")] = ''; // strip the newline if any
compare = strcmp(singleLine, word);
if (compare == 0) {
printf("n%sn", word);
}
}
fclose(file);
}
return 0;
}
add a comment |
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1 Answer
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active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
Your program only works in very special cases and has several problems:
scanf("%26s", word);
may affect up to 27 bytes in the destination array, which is defined with a length of only26
.- furthermore, you should check the return value to avoid undefined behavior on invalid input.
fopen("bin/Release/myWords.txt", "a+");
opens the file in append mode: is this necessary?
while (!feof(file))
is always wrong, you should instead check the return value offgets()
that returnsNULL
at end of file.
compare = strcmp(singleLine, word);
only compares for an exact math of the full line, which can only happen if the word has 25 characters, otherwise the trailing newline insingleLine
will cause the comparison to fail. Furthermore, broken lines may cause unexpected results, as well as if the file does not end with a newline.- the reason it matches the last word in the file is you forget to write a trailing newline after the last word in the file, so the last
fgets()
fills the buffer with the exact word and no trailing newline. - if you search for matches inside the line, you should use a larger buffer and search for a match with
strstr
. - if you search for a exact match, you should strip the trailing newline before the comparison.
Here is a modified version:
#include <stdio.h>
#include <string.h>
int main() {
char word[27];
char singleLine[256];
FILE *file = fopen("bin/Release/myWords.txt", "r");
if (scanf("%26s", word) != 1)
return 1;
if (file != NULL) {
while (fgets(singleLine, sizeof singleLine, file)) {
singleLine[strcspn(singleLine, "n")] = ''; // strip the newline if any
compare = strcmp(singleLine, word);
if (compare == 0) {
printf("n%sn", word);
}
}
fclose(file);
}
return 0;
}
add a comment |
Your program only works in very special cases and has several problems:
scanf("%26s", word);
may affect up to 27 bytes in the destination array, which is defined with a length of only26
.- furthermore, you should check the return value to avoid undefined behavior on invalid input.
fopen("bin/Release/myWords.txt", "a+");
opens the file in append mode: is this necessary?
while (!feof(file))
is always wrong, you should instead check the return value offgets()
that returnsNULL
at end of file.
compare = strcmp(singleLine, word);
only compares for an exact math of the full line, which can only happen if the word has 25 characters, otherwise the trailing newline insingleLine
will cause the comparison to fail. Furthermore, broken lines may cause unexpected results, as well as if the file does not end with a newline.- the reason it matches the last word in the file is you forget to write a trailing newline after the last word in the file, so the last
fgets()
fills the buffer with the exact word and no trailing newline. - if you search for matches inside the line, you should use a larger buffer and search for a match with
strstr
. - if you search for a exact match, you should strip the trailing newline before the comparison.
Here is a modified version:
#include <stdio.h>
#include <string.h>
int main() {
char word[27];
char singleLine[256];
FILE *file = fopen("bin/Release/myWords.txt", "r");
if (scanf("%26s", word) != 1)
return 1;
if (file != NULL) {
while (fgets(singleLine, sizeof singleLine, file)) {
singleLine[strcspn(singleLine, "n")] = ''; // strip the newline if any
compare = strcmp(singleLine, word);
if (compare == 0) {
printf("n%sn", word);
}
}
fclose(file);
}
return 0;
}
add a comment |
Your program only works in very special cases and has several problems:
scanf("%26s", word);
may affect up to 27 bytes in the destination array, which is defined with a length of only26
.- furthermore, you should check the return value to avoid undefined behavior on invalid input.
fopen("bin/Release/myWords.txt", "a+");
opens the file in append mode: is this necessary?
while (!feof(file))
is always wrong, you should instead check the return value offgets()
that returnsNULL
at end of file.
compare = strcmp(singleLine, word);
only compares for an exact math of the full line, which can only happen if the word has 25 characters, otherwise the trailing newline insingleLine
will cause the comparison to fail. Furthermore, broken lines may cause unexpected results, as well as if the file does not end with a newline.- the reason it matches the last word in the file is you forget to write a trailing newline after the last word in the file, so the last
fgets()
fills the buffer with the exact word and no trailing newline. - if you search for matches inside the line, you should use a larger buffer and search for a match with
strstr
. - if you search for a exact match, you should strip the trailing newline before the comparison.
Here is a modified version:
#include <stdio.h>
#include <string.h>
int main() {
char word[27];
char singleLine[256];
FILE *file = fopen("bin/Release/myWords.txt", "r");
if (scanf("%26s", word) != 1)
return 1;
if (file != NULL) {
while (fgets(singleLine, sizeof singleLine, file)) {
singleLine[strcspn(singleLine, "n")] = ''; // strip the newline if any
compare = strcmp(singleLine, word);
if (compare == 0) {
printf("n%sn", word);
}
}
fclose(file);
}
return 0;
}
Your program only works in very special cases and has several problems:
scanf("%26s", word);
may affect up to 27 bytes in the destination array, which is defined with a length of only26
.- furthermore, you should check the return value to avoid undefined behavior on invalid input.
fopen("bin/Release/myWords.txt", "a+");
opens the file in append mode: is this necessary?
while (!feof(file))
is always wrong, you should instead check the return value offgets()
that returnsNULL
at end of file.
compare = strcmp(singleLine, word);
only compares for an exact math of the full line, which can only happen if the word has 25 characters, otherwise the trailing newline insingleLine
will cause the comparison to fail. Furthermore, broken lines may cause unexpected results, as well as if the file does not end with a newline.- the reason it matches the last word in the file is you forget to write a trailing newline after the last word in the file, so the last
fgets()
fills the buffer with the exact word and no trailing newline. - if you search for matches inside the line, you should use a larger buffer and search for a match with
strstr
. - if you search for a exact match, you should strip the trailing newline before the comparison.
Here is a modified version:
#include <stdio.h>
#include <string.h>
int main() {
char word[27];
char singleLine[256];
FILE *file = fopen("bin/Release/myWords.txt", "r");
if (scanf("%26s", word) != 1)
return 1;
if (file != NULL) {
while (fgets(singleLine, sizeof singleLine, file)) {
singleLine[strcspn(singleLine, "n")] = ''; // strip the newline if any
compare = strcmp(singleLine, word);
if (compare == 0) {
printf("n%sn", word);
}
}
fclose(file);
}
return 0;
}
edited Nov 22 '18 at 6:58
answered Nov 20 '18 at 21:49
chqrliechqrlie
60.2k747102
60.2k747102
add a comment |
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1
see Why is “while ( !feof (file) )” always wrong?
– yano
Nov 20 '18 at 21:31
fgets
includes the final 'n`, so it gets compared along with the rest of your string.– usr2564301
Nov 20 '18 at 21:35
you need to learn how to use the debugger and use it to see the strings being compared. Until you do this you will never be able to write code.
– john elemans
Nov 20 '18 at 21:46