The problem is that the fscanf format string "%c %s %c\n" contains a trailing whitespace character (in this case \n). This whitespace character tells fscanf to read and discard all whitespace characters from the input stream until it encounters a non-whitespace character.
Therefore, when fscanf reads the lines
i hello l
abc z
it will successfully match l, hello and l, but then it will read and discard the whitespace characters "\n ". However, you only want it to read and discard "\n".
There are several ways of solving this problem:
Instead of using a whitespace character which instructs fscanf to read as many whitespace characters as possible, you can use the %*c format specifier to read and discard only a single character. However, this will only work if that character is guaranteed to be the newline character.
A more robust solution would be to first read the line using fgets instead of fscanf. In contrast to fscanf, fgets will always read exactly one entire line (if it can), so it will not leave any characters of a line on the input stream, and it also will not attempt to read characters of the next line. After reading the line and storing the line in a memory buffer as a string, you can use sscanf on that memory buffer.
Here is an example of the second solution:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
//forward function declaration
bool get_line_from_stream( char buffer[], int buffer_size, FILE *fp );
int main( void )
{
FILE *fp;
char line[200];
fp = fopen( "input.txt", "r" );
if ( fp == NULL )
{
fprintf( stderr, "Error opening file!\n" );
exit( EXIT_FAILURE );
}
while ( get_line_from_stream( line, sizeof line, fp ) )
{
char one, two[20], three;
if ( sscanf( line, "%c %19s %c", &one, two, &three ) == 3 )
{
printf(
"Successfully read the following record:\n"
" One: %c\n"
" Two: %s\n"
" Three: %c\n",
one, two, three
);
}
else
{
fprintf( stderr, "Parsing error!\n" );
}
}
fclose( fp );
}
//This function will read exactly one line of input and remove the
//newline character, if it exists. On success, it will return true.
//If this function is unable to read any further lines due to
//end-of-file, it returns false. If it fails for any other reason, it
//will not return, but will print an error message and call "exit"
//instead.
bool get_line_from_stream( char buffer[], int buffer_size, FILE *fp )
{
char *p;
//attempt to read one line from the stream
if ( fgets( buffer, buffer_size, fp ) == NULL )
{
if ( !feof(fp) )
{
fprintf( stderr, "Input error!\n" );
exit( EXIT_FAILURE );
}
return false;
}
//make sure that line was not too long for input buffer
p = strchr( buffer, '\n' );
if ( p == NULL )
{
//a missing newline character is ok if the next
//character is a newline character or if we have
//reached end-of-file
if ( !feof(fp) && getc(fp) != '\n' )
{
fprintf( stderr, "Line is too long for memory buffer!\n" );
exit( EXIT_FAILURE );
}
}
else
{
//remove newline character by overwriting it with a null
//character
*p = '\0';
}
return true;
}
For the input
a hi c
i hello l
abc z
2 mystr k
this program has the following output:
Successfully read the following record:
One: a
Two: hi
Three: c
Successfully read the following record:
One: i
Two: hello
Three: l
Successfully read the following record:
One:
Two: abc
Three: z
Successfully read the following record:
One: 2
Two: mystr
Three: k
