I wanted to write a program to check which string has a greater length without using string functions. I tried to get the two strings as input using gets() but my program keeps on crashing. Please help! Thanks!
Here's my code:
#include <stdio.h>
int l1,l2;
char *st1,*st2;
void accept()
{
gets(st1);
gets(st2);
}
void length()
{
int i = 0;
while (st1[i] != '\0')
{
l1++; i++;
}
i = 0;
while (st2[i] != '\0')
{
l1++; i++;
}
}
int main()
{
accept();
length();
if (l1 > l2)
printf("String #1 is greater in length.\n");
else
printf("String #2 is greater in length.\n");
}
you have not allocated space to st1 or st2 nor have you initialized them... so they are both pointing to some unknown place in memory. Try...
char st1[1024];
char st2[1024];
That said, realize that gets is inherently unsafe as it is subject to buffer overrun attack; there's nothing to stop someone from entering a string longer than 1024 and crashing your program.
You can also greatly simplify the length() function as follows...
void length()
{
for (l1 = 0; st1[l1] != '\0'; l1++ );
for (l2 = 0; st2[l2] != '\0'; l2++ );
}
Expanding on this and your question about what's an alternative to gets(), the answer is to use something like fgets() -- for example...
int main( int argc, char** argv )
{
if( fgets( st1, sizeof( st1 ), stdin ) != NULL )
{
if( fgets( st2, sizeof( st2 ), stdin ) != NULL )
{
length();
if (l1 > l2) printf("String #1 is greater in length.\n");
else if (l2 > l1) printf("String #2 is greater in length.\n");
else printf( "Both strings are the same length.\n" );
}
else printf( "could not read second string\n" );
}
else printf( "could not read first string\n" );
return( 0 );
}
In this case, fgets() will not allow the user to overflow st1 or st2 and it will ensure they are always null terminated strings.
use l2 in the second while loop,
l1=0;
while (st1[l1] != '\0')
{
l1++;
}
l2 = 0;
while (st2[l2] != '\0')
{
l2++;
}
Related
hi i am a trying to make the console read characters and increase the size with realloc until i hit ctr+z and end the loop.The terminal is displayng segmentation fault.The program should work like this:
f
f
f
f
f
f
Hit ctrl + z
print the characters.
How to fix this?
#include <stdio.h>
#include <stdlib.h>
int main()
{
int size = 2;
char* buffer = NULL;
buffer = (char*) malloc(size*sizeof(char));
if(buffer==NULL)
{
puts("Allocation failed");
}
printf("Enter character: ");
while(1)
{
buffer = getchar();
size++;
buffer = (char*) realloc(buffer,size*sizeof(char));
if(buffer==NULL)
{
puts("Allocation failed");
}
}
printf("%c",buffer);
free(buffer);
}
buffer = getchar(); should be giving you compiler warnings...
getchar() returns an int and this clobbers the pointer to the allocated heap memory... You want some kind of indexing or something to put the character into the buffer, not slam the buffer's address..
You're struggling with this. It's important to note that realloc( NULL ... acts just like malloc(), so you can "grow" the array from zero as needed calling realloc from just one location.
#include <stdio.h>
#include <stdlib.h>
int main() {
int ch, size = 0; // trust me
char *buffer = NULL;
printf( "Enter characters: " );
while( ( ch = getchar() ) != EOF ) {
char *tmp = (char*)realloc( buffer, (size+1) * sizeof *tmp );
if( tmp == NULL ) {
puts( "Allocation failed" );
exit( 1 );
}
buffer = tmp; // the possibly new memory address
buffer[ size++ ] = (char)ch; // the new character just entered.
}
// NB: buffer is NOT a null terminated C string.
// It is an array of characters that can be printed, though.
printf( "\nGot this: %.*s", size, buffer );
return 0;
}
Enter characters: Quick Brown Foxes ^Z
Got this: Quick Brown Foxes
Instead of this:
buffer = getchar();
This:
*buffer = getchar();
But you should also support detecting for EOF in case of redirected input:
while(1)
{
int result = getchar();
if (result == EOF)
{
break;
}
*buffer = (char)result;
I’m trying to read text from stdin line by line using fgets() and store the text in a variable “text”. However, when I use strtok() to split the words, it only works for a couple lines before terminating. What should I change to make it run through the entire text?
#define WORD_BUFFER_SIZE 50
#define TEXT_SIZE 200
int main(void) {
char stopWords[TEXT_SIZE][WORD_BUFFER_SIZE];
char word[WORD_BUFFER_SIZE];
int numberOfWords = 0;
while(scanf("%s", word) == 1){
if (strcmp(word, "====") == 0){
break;
}
strcpy(stopWords[numberOfWords], word);
numberOfWords++;
}
char *buffer = malloc(sizeof(WORD_BUFFER_SIZE)*TEXT_SIZE);
char *text = malloc(sizeof(WORD_BUFFER_SIZE)*TEXT_SIZE);
while(fgets(buffer, WORD_BUFFER_SIZE*TEXT_SIZE, stdin) != NULL){
strcat(text, buffer);
}
char *k;
k = strtok(text, " ");
while (k != NULL) {
printf("%s\n", k);
k = strtok(NULL, " ");
}
}
char *buffer = malloc(sizeof(WORD_BUFFER_SIZE)*TEXT_SIZE);
char *text = malloc(sizeof(WORD_BUFFER_SIZE)*TEXT_SIZE);
sizeof(WORD_BUFFER_SIZE) is a constant, it's the size of integer. You probably mean WORD_BUFFER_SIZE * TEXT_SIZE. But you can find the file size and calculate exactly how much memory you need.
char *text = malloc(...)
strcat(text, buffer);
text is not initialized and doesn't have a null-terminator. strcat needs to know the end of text. You have to set text[0] = '\0' before using strcat (it's not like strcpy)
int main(void)
{
fseek(stdin, 0, SEEK_END);
size_t filesize = ftell(stdin);
rewind(stdin);
if (filesize == 0)
{ printf("not using a file!\n"); return 0; }
char word[1000] = { 0 };
//while (scanf("%s", word) != 1)
// if (strcmp(word, "====") == 0)
// break;
char* text = malloc(filesize + 1);
if (!text)
return 0;
text[0] = '\0';
while (fgets(word, sizeof(word), stdin) != NULL)
strcat(text, word);
char* k;
k = strtok(text, " ");
while (k != NULL)
{
printf("%s\n", k);
k = strtok(NULL, " ");
}
return 0;
}
According to the information you provided in the comments section, the input text is longer than 800 bytes.
However, in the line
char *text = malloc(sizeof(WORD_BUFFER_SIZE)*TEXT_SIZE);
which is equivalent to
char *text = malloc(800);
you only allocated 800 bytes as storage for text. Therefore, you did not allocate sufficient space to store the entire input into text. Attempting to store more than 800 bytes will result in a buffer overflow, which invokes undefined behavior.
If you want to store the entire input into text, then you must ensure that it is large enough.
However, this is probably not necessary. Depending on your requirements, it is probably sufficient to process one line at a time, like this:
while( fgets( buffer, sizeof buffer, stdin ) != NULL )
{
char *k = strtok( buffer, " " );
while ( k != NULL )
{
printf( "%s\n", k );
k = strtok( NULL, " " );
}
}
In that case, you do not need the array text. You only need the array buffer for storing the current contents of the line.
Since you did not provide any sample input, I cannot test the code above.
EDIT: Based on your comments to this answer, it seems that your main problem is how to read in all of the input from stdin and store it as a string, when you do not know the length of the input in advance.
One common solution is to allocate an initial buffer, and to double its size every time it gets full. You can use the function realloc for this:
#include <stdio.h>
#include <stdlib.h>
int main( void )
{
char *buffer;
size_t buffer_size = 1024;
size_t input_size = 0;
//allocate initial buffer
buffer = malloc( buffer_size );
if ( buffer == NULL )
{
fprintf( stderr, "allocation error!\n" );
exit( EXIT_FAILURE );
}
//continuously fill the buffer with input, and
//grow buffer as necessary
for (;;) //infinite loop, equivalent to while(1)
{
//we must leave room for the terminating null character
size_t to_read = buffer_size - input_size - 1;
size_t ret;
ret = fread( buffer + input_size, 1, to_read, stdin );
input_size += ret;
if ( ret != to_read )
{
//we have finished reading from input
break;
}
//buffer was filled entirely (except for the space
//reserved for the terminating null character), so
//we must grow the buffer
{
void *temp;
buffer_size *= 2;
temp = realloc( buffer, buffer_size );
if ( temp == NULL )
{
fprintf( stderr, "allocation error!\n" );
exit( EXIT_FAILURE );
}
buffer = temp;
}
}
//make sure that `fread` did not fail end due to
//error (it should only end due to end-of-file)
if ( ferror(stdin) )
{
fprintf( stderr, "input error!\n" );
exit( EXIT_FAILURE );
}
//add terminating null character
buffer[input_size++] = '\0';
//shrink buffer to required size
{
void *temp;
temp = realloc( buffer, input_size );
if ( temp == NULL )
{
fprintf( stderr, "allocation error!\n" );
exit( EXIT_FAILURE );
}
buffer = temp;
}
//the entire contents is now stored in "buffer" as a
//string, and can be printed
printf( "contents of buffer:\n%s\n", buffer );
free( buffer );
}
The code above assumes that the input will be terminated by an end of file condition, which is probably the case if the input is piped from a file.
On second thought, instead of having one large string for the whole file, as you are doing in your code, you may rather want an array of char* to the individual strings, each representing a line, so that for example lines[0] will be the string of the first line, lines[1] will be the string of the second line. That way, you can easily use strstr to find the " ==== " deliminator and strchr on each individual line to find the individual words, and still have all the lines in memory for further processing.
I don't recommend that you use strtok in this case, because that function is destructive in the sense that it modifies the string, by replacing the deliminators with null characters. If you require the strings for further processing, as you stated in the comments section, then this is probably not what you want. That is why I recommend that you use strchr instead.
If a reasonable maximum number of lines is known at compile-time, then the solution is rather easy:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_LINE_LENGTH 1024
#define MAX_LINES 1024
int main( void )
{
char *lines[MAX_LINES];
int num_lines = 0;
char buffer[MAX_LINE_LENGTH];
//read one line per loop iteration
while ( fgets( buffer, sizeof buffer, stdin ) != NULL )
{
int line_length = strlen( buffer );
//verify that entire line was read in
if ( buffer[line_length-1] != '\n' )
{
//treat end-of file as equivalent to newline character
if ( !feof( stdin ) )
{
fprintf( stderr, "input line exceeds maximum line length!\n" );
exit( EXIT_FAILURE );
}
}
else
{
//remove newline character from string
buffer[--line_length] = '\0';
}
//allocate memory for new string and add to array
lines[num_lines] = malloc( line_length + 1 );
//verify that "malloc" succeeded
if ( lines[num_lines] == NULL )
{
fprintf( stderr, "allocation error!\n" );
exit( EXIT_FAILURE );
}
//copy line to newly allocated buffer
strcpy( lines[num_lines], buffer );
//increment counter
num_lines++;
}
//All input lines have now been successfully read in, so
//we can now do something with them.
//handle one line per loop iteration
for ( int i = 0; i < num_lines; i++ )
{
char *p, *q;
//attempt to find the " ==== " marker
p = strstr( lines[i], " ==== " );
if ( p == NULL )
{
printf( "Warning: skipping line because unable to find \" ==== \".\n" );
continue;
}
//skip the " ==== " marker
p += 6;
//split tokens on remainder of line using "strchr"
while ( ( q = strchr( p, ' ') ) != NULL )
{
printf( "found token: %.*s\n", (int)(q-p), p );
p = q + 1;
}
//output last token
printf( "found token: %s\n", p );
}
//cleanup allocated memory
for ( int i = 0; i < num_lines; i++ )
{
free( lines[i] );
}
}
When running the program above with the following input
first line before deliminator ==== first line after deliminator
second line before deliminator ==== second line after deliminator
it has the following output:
found token: first
found token: line
found token: after
found token: deliminator
found token: second
found token: line
found token: after
found token: deliminator
If, however, there is no reasonable maximum number of lines known at compile-time, then the array lines will also have to be designed to grow in a similar way as buffer in the previous program. The same applies for the maximum line length.
I'm trying to convert a string from upper case to lower case to check if it is a palindrome, however I keep getting the error:
"function declaration is not a prototype"
I already added #include <string.h> in the header, but it still doesn't work. How do I get around this issue?
This is the code:
int main (void)
{
char *user_string, *user_string_rev;
/* the malloc function is used to make sure that enough memory is allocated for the string and that it does not overwrite memory boxes of other variables. */
user_string= (char*)malloc(BUFF_SIZE*sizeof(char));
user_string_rev= (char*)malloc(BUFF_SIZE*sizeof(char));
printf("Please enter a string:");
fgets(user_string,BUFF_SIZE, stdin); /* fgets function take the string the user inputs and stores it into user_string. */
user_string_rev=strcpy(user_string_rev, user_string); /*the strcpy takes the string the user inputs and copies it to user_string_rev. */
strlwr(user_string_rev);
palindrome_check(user_string,user_string_rev); /*this is the palindrome function used to check if the two strings are palindromes, it intakes two arguments, the two strings and does not return anything. */
return 0;
}
Replace :
strlwr(user_string_rev);
which is not a standard function with:
int i = 0;
while (user_string_rev[i])
{
if (isalpha(user_string_rev[i]))
user_string_rev[i] |= 32;
++i;
}
Don't forget to add the ctype header at the top of your .c file to use isalpha:
#include <ctype.h>
the following proposed code:
incorporates the comments to the question
cleanly compiles
properly checks for errors
will treat a string that is nothing but a newline as NOT a palindrome
And now the proposed code:
#include <stdio.h> // getline(), printf()
#include <stdlib.h> // free()
#include <ctype.h> // tolower()
#include <string.h> // strlen(), strchr()
// prototypes
void palindrome( char *, size_t length );
int main( void )
{
char *inputStr = NULL;
size_t lengthStr = 0;
printf("Please enter a string:");
if( -1 != getline( &inputStr, &lengthStr, stdin ) )
{
size_t length = strlen( inputStr );
for( size_t i = 0; i < length; i++ )
{
inputStr[i] = (char)tolower( inputStr[i] );
}
char *newline = strchr( inputStr, '\n' );
if( newline )
{
*newline = '\0';
length--;
}
palindrome( inputStr, length );
}
free( inputStr );
return 0;
}
void palindrome( char stringToCheck[], size_t length )
{
size_t index = length - 1; // don't check NUL terminator byte
size_t i;
for( i = 0; i < index; i++ )
{
if( stringToCheck[i] != stringToCheck[ index ] )
{
break;
}
index--;
}
if( i < index )
{
printf( "%s is not a palindrome\n", stringToCheck );
}
else
{
printf( "%s is a palindrome\n", stringToCheck );
}
}
Hi I'm trying to figure how to count characters in comments in c program. So far i had written a function that doesn't work, but seems logical. Can you please help me complete my task.My quest is to fill buffer with all the characters from the comments and then count them.
void FileProcess3(char* FilePath)
{
char myString [1000];
char buffer[1000];
FILE* pFile;
int i = 0;
pFile = fopen (FilePath, "r");
while(fgets( myString, 1000, pFile) != NULL)
{
int jj = -1;
while(++jj < strlen(myString))
{
if ( myString[jj] == '/' && myString[jj+1] == '*')
{
check = 1;
jj++;
jj++;
}
if( check == 1 )
{
if ( myString[jj] == '*' && myString[jj+1] == '/')
{
check = 0;
break;
}
strcat( buffer, myString[jj] );
}
}
}
printf(" %s ", buffer );
fclose(pFile);
}
E.g. fix to
int i = 0, check = 0;
...
if( check == 1 )
{
if ( myString[jj] == '*' && myString[jj+1] == '/')
{
check = 0;
break;
}
buffer[i++] = myString[jj];
}
}
}
buffer[i]='\0';/* add */
strcat() concatenates (NUL-terminated) strings, so this is definitely wrong
(and should give a compiler warning due to the wrong type of the second argument):
strcat( buffer, myString[jj]);
You could do something like
buffer[length] = myString[jj];
buffer[length+1] = 0;
length++;
where length is an integer initialized to zero that keeps track of the current length.
Of course you should check the length against the available size of the buffer
to avoid a buffer(!) overflow.
If your intention is only to count the characters, then you don't have to copy
them to a separate buffer at all. Just increment a counter.
You should also note that fgets() does not remove the newline characters from the
input. So you have to check for that if you don't want to include the newlines
in the count.
#include <stdio.h>
#include <ctype.h>
int isPalindrome( char *str, int length )
{
if ( length < 1 )
{
return 1; /* no more chars to compare, its a palindrome */
}
if ( str[0] == str[length-1] ) /* Are the two ends same? */
{
return isPalindrome( str+1, length-2 ); /* continue checking */
}
else
{
return 0; /* comparison failed, not a palindrome */
}
}
void strToUpper( char *src )
{
/* convet to upper case any letter */
while( ( *src = toupper( *src ) ) != '\0' )
{
++src;
}
}
int main( void )
{
int result = 0;
char str[40] = { '\0' };
printf( "Please type the string to identify Palindrom or not: ", stdout );
fflush( stdout );
fgets( str, sizeof str, stdin );
strToUpper( str ); /* make all letters the same for comparison */
result = isPalindrome( str, ( strlen( str ) - 1 ) ); /* recursive starts here */
if( result == 1 )
{
printf( "1" );
}
else
{
printf( "0" );
}
getchar();
return 0;
}
I wrote this code which identifies palidromes in C, but I want to use scanf instead of fputs or fgets, so I can understand the other way to solve this problem.
There is no fputs and only a single call to fgets in this code.
The method of input here really don't affect "way to solve this problem". It's the same code - changing one line won't change lot. scanf not a safe function. You can do scanf("%s", str) but fgets is better and recommended. If you need to analyze string after fgets, you can use sscanf.