I am just not sure why my replaceWord isn't going in to the file at all i have used all the commented out and so on and so forth. I am just trying to replace with with the text received from the command line argument. I know i might be far off I was just looking for a relatively easy way to do it.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main ( int argc, char *argv[] )
{
if ( argc != 4 ) /* argc should be 2 for correct execution */
{
/* We print argv[0] assuming it is the program name */
printf( "usage: %s filename\n", argv[0] );
}
else
{
// We assume argv[1] is a filename to open
char* wordReplace = argv[1];
char* replaceWord = argv[2];
FILE *file = fopen( argv[3], "r" );
/* fopen returns 0, the NULL pointer, on failure */
if ( file == 0 )
{
printf( "Could not open file\n" );
}
else
{
char string[100];
int len = 0;
/* read one character at a time from file, stopping at EOF, which
indicates the end of the file. Note that the idiom of "assign
to a variable, check the value" used below works because
the assignment statement evaluates to the value assigned. */
while ( (fscanf( file, "%s", string ) ) != EOF )
{
len = strlen(string);
printf( "%s\n", string );
if(strcmp(string, wordReplace) == 0){
//fseek (file, (-strlen(string) + 1), 1);
//fputc(*replaceWord,file);
//replaceWord++;
//strcpy(string, replaceWord);
fprintf(file,"%s",replaceWord);
fputs(replaceWord, file);
printf("\n%d\n", len);
}
}
fclose( file );
}
}
printf("\n");
return 0;
}
You've opened the file in r ie read mode and trying to write to it.
Also after correcting that, note that, the replaced word and word to be replaced have to be of the same size, if you want to replace the file in place. Else you will end up overwriting other data. And you need to use functions like fseek to reposition the internal file pointer as fp would have moved ahead after fscanf
Related
I have a file .txt with values of some variable. I need to read them to declarate my variables in main. What is wrong?
#include <stdio.h>
#define INPUT "input.txt"
int main (void){
FILE *open_file = fopen(INPUT, "r");
if (open_file == NULL){
puts("ERROR.");
} else {
puts("SUCCESS.");
}
char *buffer;
int size = ftell(open_file);
int read_file = fread(buffer,size,*open_file);
int Integer1, Integer2;
while (size != EOF){
sscanf("%d%d",Integer1, Integer2);
}
int close_file = fclose(open_file);
if (close_file == -1){
puts("Error in closing file.");
} else {
puts("Closing file: SUCCESS.");
}
return 0;
}
Whats is wrong? I have to read every line of my file. For example if my file contains:
1
2
My scanf should set:
Integer1 = 1;
Integer2 = 2;
One problem is that after the line
char *buffer;
the variable buffer does not point to any valid memory location. It is a wild pointer.
You can either create a fixed size array like this:
char buffer[100];
or you can create a dynamically sized memory buffer, like this:
if ( fseek( open_file, 0, SEEK_END ) != 0 )
DoSomethingToHandleError();
long size = ftell(open_file);
if ( fseek( open_file, 0, SEEK_SET ) != 0 )
DoSomethingToHandleError();
char *buffer = malloc( size );
if ( buffer == NULL )
DoSomethingToHandleError();
Depending on whether you used a fixed-size array or a dynamically allocated buffer, you should change the call to fread to one of the following:
fread( buffer, sizeof(buffer), open_file ); //for fixed size array
fread( buffer, size, open_file ); //for dynamically allocated buffer
Instead of using the function fread, you would probably be better off using the function fgets, especially because sscanf requires a null-terminated string as input, not binary data. The function fread will give you binary data that is not null-terminated, whereas fgets will give you a null-terminated string.
Also, change the line
sscanf("%d%d",Integer1, Integer2);
to
sscanf( buffer, "%d%d", &Integer1, &Integer2);
Before using Integer1 and Integer2 afterwards, you should also check the return value of sscanf to make sure that both integers were found in the string.
However, if you don't want to handle the memory management and reading in of the file yourself, you can simply use fscanf, like this:
if ( fscanf( open_file, "%d%d", &Integer1, &Integer2 ) != 2 )
DoSomethingToHandleError();
But this has the disadvantage that fscanf will just give you the first two numbers that it finds in the file, and won't perform much input validation. For example, fscanf won't enforce that the two numbers are on separate lines. See the following link for more information on the disadvantages of using fscanf:
A beginners' guide away from scanf()
If you use the function fgets as I suggested, then you will need two calls to fgets to read both lines of the file. This means that sscanf will be unable to find both integers in the same string. Therefore, if you use fgets, then you will have to change your program logic a bit, for example like this:
#define MAX_INTEGERS 2
char buffer[100];
int integers[MAX_INTEGERS];
int num_found = 0;
while ( fgets( buffer, sizeof(buffer), open_file ) != NULL )
{
int i;
if ( strchr( buffer, '\n' ) == NULL && !feof( openfile ) )
{
printf( "Error: Line size too long! Aborting.\n" );
break;
}
if ( sscanf( buffer, "%d", &i ) == 1 )
{
if ( num_found == MAX_INTEGERS )
{
printf(
"Error: Found too many integers in file! This "
"program only has room for storing %d integers. "
"Aborting.\n",
MAX_INTEGERS
);
break;
}
//add found integer to array and increment num_found
integers[num_found++] = i;
}
else
{
printf(
"Warning: Line without number encountered. This could "
"simply be a harmless empty line at the end of the "
"file, but could also indicate an error.\n"
);
}
}
printf( "Found the following integers:\n" );
for ( int i = 0; i < num_found; i++ )
{
printf( "%d\n", integers[i] );
}
Instead of using sscanf, you may want to use strtol, as that function allows you to perform stricter input validation.
If you don't want to use the function fgets, which reads input line by line, but really want to read the whole file at once using fread, you can do that, but you would have to add the terminating null character manually.
EDIT: Since you stated in the comments that you didn't want a loop and wanted to store the individual lines each into their own named variable, then you could use the following code instead:
//This function will assume that one number is stored per line, and
//write it to the memory location that "output" points to. Note that
//the return value does not specify the number found, but rather
//whether an error occurred or not. A return value of 0 means no error,
//nonzero means an error occurred.
int get_number( FILE *fp, int *output )
{
char buffer[100];
int i;
//read the next line into buffer and check for error
if ( fgets( buffer, sizeof(buffer), fp ) == NULL )
return -1;
//make sure line was not too long to fit into buffer
if ( strchr( buffer, '\n' ) == NULL && !feof( fp ) )
return -1;
//parse line and make sure that a number was found
if ( sscanf( buffer, "%d", &i ) != 1 )
return -1;
*output = i
return 0;
}
Now, in your function main, you can simply use the following code:
int error_occurred = 0;
if ( get_number( &Integer1 ) != 0 )
{
printf( "Error occured when reading the first integer.\n" );
error_occurred = 1;
}
if ( get_number( &Integer2 ) != 0 )
{
printf( "Error occured when reading the second integer.\n" );
error_occurred = 1;
}
if ( !error_occurred )
{
printf( "The value of Integer1 is: %d\n", Integer1 );
printf( "The value of Integer2 is: %d\n", Integer2 );
}
There are couple of problems in your code
fread(buffer,size,*open_file);, buffer is not allocated
A) you have to allocate memory using malloc or calloc if you use pointers and also free after you are done with it.
If you want to avoid the headache of allocating and freeing, you better use an array sufficient enough to store the contents.
fread takes 4 arguments
A) 4th argument is not FILE , its FILE* , use only open_file not *open_file and you have not used nmemb(number of members) parameter
On success, fread() return the number of items read, so check the return value to avoid errors.
ftell() returns the current offset , Otherwise, -1 is returned
A) you really don't need it, check the return value of fread to find out you have reached the EOF.
check the syntax of sscanf and example
OP's code failed to seek the end of the array, allocate space for buffer and used fread() incorrectly.
Correct version shown with some error checking.
//char *buffer;
//int size = ftell(open_file);
//int read_file = fread(buffer,size,*open_file);
// Seek and report, hopefully, the end position
if (fseek(open_file, 0, SEEK_END)) { fprintf(stderr, "fseek() failed.\n"); return EXIT_FAILURE;
long size = ftell(open_file);
if (size == -1) { fprintf(stderr, "ftell() failed.\n"); return EXIT_FAILURE; }
// Allocate memory and read
if ((unsigned long) size > SIZE_MAX) { fprintf(stderr, "size too big.\n"); return EXIT_FAILURE; }
char *buffer = malloc((size_t) size);
if (buffer == NULL) { fprintf(stderr, "malloc() failed.\n"); return EXIT_FAILURE; }
size_t length = fread(buffer, sizeof *buffer, size, open_file);
// Use `length` as the number of char read
// ...
// when done
free(buffer);
Other problems too.
// while (size != EOF){
// sscanf("%d%d",Integer1, Integer2);
// }
Maybe later, GTG.
I'm having some problems with this little function that can read a file:
void ReadFile(char *name) {
FILE *fr;
int lenght, i;
fr = fopen(name, "r"); //Open the file reader
fseek(fr, 0, 2); //Set the pointer at the EOF
lenght = ftell(fr); //Read the ending position
printf("\nDEBUG lenght:%d\n", lenght);
fseek(fr, 0, 0); //Return at the beginning of the file
printf("File read:\n\n");
for (i = 1; i <= lenght; i++) {
printf("%c", getc(fr));
fseek(fr, i, 0);
}
fclose(fr);
}
This is the file that it reads:
qwerty
asdfgh
zxcvbn
But this is the output of the program:
DEBUG lenght:24
File read:
qwerty
asdfgh
zxcvbn
It is basically reading an extra "\n" when there is one before.
Any ideas of why the code doesn't work?
Thanks
If you open a file in text mode (as you do), then a call to fseek may only contain offset values that have been previously retrieved by an ftell function (cf, for example, cppreference/fseek):
If the stream is open in text mode, the only supported values for
offset are zero (which works with any origin) and a value returned by
an earlier call to ftell on a stream associated with the same file
(which only works with origin of SEEK_SET).
In your for-loop, however, you are passing the value of i, which is not retrieved by ftell.
Besides that, your fseek in the loop is superflous, as fgetc moves the read pointer forward anyway. So for (i = 1; i <= lenght; i++) { printf("%c", getc(fr)); } should do the job.
the following proposed code:
cleanly compiles
performs the desired functionality
properly checks for errors
and now, the proposed code:
#include <stdio.h> // EOF, fopen(), getc(), putc() fclose() puts() perror()
#include <stdlib.h> // exit(), EXIT_FAILURE
// prototype
void ReadFile(char *filename);
void ReadFile(char *filename)
{
FILE *fp = fopen( filename, "r" );
if( !fp )
{
perror( "fopen failed" );
exit( EXIT_FAILURE );
}
// implied else, fopen successful
puts("File read:\n");
int ch;
while( (ch = getc( fp )) != EOF )
{
putchar( ch );
}
fclose(fp);
}
So I am writing a program in C that takes in a few command-line arguments and also reads a file and prints it to standard out. This is my code thus far:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main( int argc, char* argv[] ) {
char* file_path;
float a;
float b;
char filedata[200];
if (argc != 4) {
printf("Error: 4 arguments are required.\n");
return -1;
}
file_path = argv[1];
a = atof(argv[2]);
b = atof(argv[3]);
if( a == 0.0 ) {
printf("Error: bad float arg\n");
return -1;
}
if( b == 0.0 ) {
printf("Error: bad float arg\n");
return -1;
}
FILE* fp = fopen( file_path, "r");
if( fp == NULL ){
printf( "Error: bad file; %s\n", file_path);
return -1;
}
while( fgets( filedata, 200, fp ) ){
printf("%s", filedata);
}
fclose(fp);
}
At the very bottom I have began to read a file. What I am trying to do is find files that contain the characters "#A#" and "#B#" and then print an error message when files containing these characters are not present.
Unfortunately, a simple if statement will not work in this scenario as I am not checking for equality but rather whether or not something is present.
If anybody could tell me about any C functions that are able to read and check the contents of a file, along with a few more specifics, then I would highly appreciate it!
After taking each line (into 'filedata') simply use the strstr function to check if it contains that substring "#A#" etc.
if strstr finds the substring it will return a pointer to it, otherwise it will return a NULL pointer.
So you should write something like this:
if ( strstr(filedata, "#A#") == NULL )
printf("Error\n");
but since you are looking at the entire file for this substring, you need to check all the lines before you conclude that there is an error.
There are no compile errors just functionality
I was attempting to make a simple XOR crypter in c. I found out that the crypting part is not a problem because when the XOR function is used twice on the same string it returns the the exact string I sent back. The problem I believe is therefore not with the crypting part, I believe that the problem occurs when writing the file.
Function the error is within
int xorFile (char *infile, char *outfile) {
FILE *in,
*out;
long lSize;
char *buffer;
in = fopen ( infile , "rb" );
out = fopen(outfile, "wb");
if( !in ) perror(infile),exit(1);
fseek( in , 0L , SEEK_END);
lSize = ftell( in );
rewind( in );
/* allocate memory for entire content */
buffer = (char*)calloc( 1, lSize+1 );
if( !buffer ) fclose(in),fputs("memory alloc fails",stderr),exit(1);
/* copy the file into the buffer */
if( 1!=fread( buffer , lSize, 1 , in) )
fclose(in),free(buffer),fputs("entire read fails",stderr),exit(1);
/* do your work here, buffer is a string contains the whole text */
int i;
for(i=0;buffer[i]!='\0';i++) {
fputc(buffer[i] ^ XOR_KEY,out);
}
fclose(in);
free(buffer);
fclose(out);
return 0;
}
What I believe causes the error
int i;
for(i=0;buffer[i]!='\0';i++) {
fputc(buffer[i] ^ XOR_KEY,out);
}
Full Program
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/stat.h>
#define XOR_KEY 0x6F
int xorFile (char *infile, char *outfile) {
FILE *in,
*out;
long lSize;
char *buffer;
in = fopen ( infile , "rb" );
out = fopen(outfile, "wb");
if( !in ) perror("blah.txt"),exit(1);
fseek( in , 0L , SEEK_END);
lSize = ftell( in );
rewind( in );
/* allocate memory for entire content */
buffer = (char*)calloc( 1, lSize+1 );
if( !buffer ) fclose(in),fputs("memory alloc fails",stderr),exit(1);
/* copy the file into the buffer */
if( 1!=fread( buffer , lSize, 1 , in) )
fclose(in),free(buffer),fputs("entire read fails",stderr),exit(1);
/* do your work here, buffer is a string contains the whole text */
int i;
for(i=0;buffer[i]!='\0';i++) {
fputc(buffer[i] ^ XOR_KEY,out);
}
fclose(in);
free(buffer);
fclose(out);
return 0;
}
int main (int argc, char *argv[]) {
if (argc <= 2) {
fprintf (stderr, "Usage: %s [IN FILE] [OUT FILE]\n" , argv[0]) ;
exit (1);
}
xorFile (argv[1], argv[2]) ;
}
Tested causes
Checked on multiple OS's
Checked on different file formats
Checked on different privileges
Checked on different compilers as well(ran out of things to test)
Additional infomation
When I encrypted a copy of the source file and decrypted it, all that remained was #include <std
The problem you're experiencing is caused by your loop exiting prematurely. The following test will stop as soon as it encounters a null byte:
for(i=0;buffer[i]!='\0';i++)
To encrypt the entire file, this needs to be changed to:
for(i=0;i<lSize;i++)
This will be a problem not only for non-text files, but also for decrypting, since the encryption process will introduce zero bytes for any characters that match your XOR_KEY. For instance, if your XOR_KEY is 0x69, which is an ascii 'i', your encrypted file will contain a zero byte in place of each 'i'. When decrypting it, it will cut the file off at the first such character, which explains what you've been seeing. This will correct that.
buffer[i] ^= XOR_KEY;
fputc(buffer[i] ^ XOR_KEY,out);
First, the program looks at the character in buffer[i], XORs it, and stores the XORed character back in buffer[i].
Then, it looks at the character in buffer[i] (which is now XORed), XORs it again, and writes that to out.
So the character that gets written to out has been XORed twice - so it's just the original character.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main ( int argc, char *argv[] )
{
if ( argc != 4 ) /* argc should be 4 for correct execution */
{
/* Print argv[0] assuming it is the program name */
printf( "usage: %s filename\n", argv[0] );
}
else
{
// We assume argv[1] is a filename to open
char* wordReplace = argv[1];
char* replaceWord = argv[2];
FILE *file = fopen( argv[3], "r+" );
/* fopen returns 0, the NULL pointer, on failure */
if ( file == 0 )
{
printf( "Could not open file\n" );
}
else
{
char string[100];
int len = 0;int count = 0;int i = 0;int k = 0;
while ( (fscanf( file, "%s", string ) ) != EOF )
{
len = strlen(string);
count++;
char charray[len+1];
if(count == 1)
{
for (i = 0; i < len; i++)
{
charray[i] = replaceWord[i];
printf("%c\n", charray[i]);
}
}
//printf("%c\n", charray[0]);
printf( "%s\n", string );
if(strcmp(string, wordReplace) == 0)
{
for(k = 0; k < strlen(replaceWord); k++)
{
fseek (file, (-(long)len), SEEK_CUR);
fputc(charray[k],file);
//replaceWord++;
}
//strcpy(string, replaceWord);
//fprintf(file,"%s",replaceWord);
//fputs(string, file);
//printf("\n%d\n", len);
}
}
fclose( file );
}
}
printf("\n");
return 0;
}
This code currently works in replacing the First word properly, but if there are multiple words that i want overwritten with the replace word or the word appears somewhere else in the text it will not properly change it, and it will change it to ram trash etc. I was curious if anyone could lead me to a reason why thank you.
Assuming the words are the same length (if not you have quite a few more issues):
Let's say you have a 4 character word:
fseek (file, (-(long)len), SEEK_CUR); will go back to position 0 (4-4), fputc(charray[k],file); will update to position 1, then you back 4 more which is an error but since you're not checking the return value from fseek you will not know this. At this point the algorithm is not working any more since your assumed file positions are all wrong
EDIT:
if(strcmp(string, wordReplace) == 0)
{
fseek (file, (-(long)len), SEEK_CUR);
for(k = 0; k < strlen(replaceWord); k++)
{
fputc(charray[k],file);
}
}
fflush(file); //you need to flush the file since you are switching from write to read
EDIT 2: reason for flush: from 4.5.9.2 ANSI C, similar paragraph in C99 7.19.5.3):
When a file is opened with update mode ('+' as the second or third character in the mode argument), both input and output may be performed on the associated stream. However, output may not be directly followed by input without an intervening call to the fflush function or to a file positioning function ( fseek , fsetpos , or rewind ), and input may not be directly followed by output without an intervening call to a file positioning function, unless the input operation encounters end-of-file.
Between the read and write you have the fseek already so that is not a problem