Related
I wrote this function to read a line from a file:
const char *readLine(FILE *file) {
if (file == NULL) {
printf("Error: file pointer is null.");
exit(1);
}
int maximumLineLength = 128;
char *lineBuffer = (char *)malloc(sizeof(char) * maximumLineLength);
if (lineBuffer == NULL) {
printf("Error allocating memory for line buffer.");
exit(1);
}
char ch = getc(file);
int count = 0;
while ((ch != '\n') && (ch != EOF)) {
if (count == maximumLineLength) {
maximumLineLength += 128;
lineBuffer = realloc(lineBuffer, maximumLineLength);
if (lineBuffer == NULL) {
printf("Error reallocating space for line buffer.");
exit(1);
}
}
lineBuffer[count] = ch;
count++;
ch = getc(file);
}
lineBuffer[count] = '\0';
char line[count + 1];
strncpy(line, lineBuffer, (count + 1));
free(lineBuffer);
const char *constLine = line;
return constLine;
}
The function reads the file correctly, and using printf I see that the constLine string did get read correctly as well.
However, if I use the function e.g. like this:
while (!feof(myFile)) {
const char *line = readLine(myFile);
printf("%s\n", line);
}
printf outputs gibberish. Why?
If your task is not to invent the line-by-line reading function, but just to read the file line-by-line, you may use a typical code snippet involving the getline() function (see the manual page here):
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
FILE * fp;
char * line = NULL;
size_t len = 0;
ssize_t read;
fp = fopen("/etc/motd", "r");
if (fp == NULL)
exit(EXIT_FAILURE);
while ((read = getline(&line, &len, fp)) != -1) {
printf("Retrieved line of length %zu:\n", read);
printf("%s", line);
}
fclose(fp);
if (line)
free(line);
exit(EXIT_SUCCESS);
}
FILE* filePointer;
int bufferLength = 255;
char buffer[bufferLength]; /* not ISO 90 compatible */
filePointer = fopen("file.txt", "r");
while(fgets(buffer, bufferLength, filePointer)) {
printf("%s\n", buffer);
}
fclose(filePointer);
In your readLine function, you return a pointer to the line array (Strictly speaking, a pointer to its first character, but the difference is irrelevant here). Since it's an automatic variable (i.e., it's “on the stack”), the memory is reclaimed when the function returns. You see gibberish because printf has put its own stuff on the stack.
You need to return a dynamically allocated buffer from the function. You already have one, it's lineBuffer; all you have to do is truncate it to the desired length.
lineBuffer[count] = '\0';
realloc(lineBuffer, count + 1);
return lineBuffer;
}
ADDED (response to follow-up question in comment): readLine returns a pointer to the characters that make up the line. This pointer is what you need to work with the contents of the line. It's also what you must pass to free when you've finished using the memory taken by these characters. Here's how you might use the readLine function:
char *line = readLine(file);
printf("LOG: read a line: %s\n", line);
if (strchr(line, 'a')) { puts("The line contains an a"); }
/* etc. */
free(line);
/* After this point, the memory allocated for the line has been reclaimed.
You can't use the value of `line` again (though you can assign a new value
to the `line` variable if you want). */
//open and get the file handle
FILE* fh;
fopen_s(&fh, filename, "r");
//check if file exists
if (fh == NULL){
printf("file does not exists %s", filename);
return 0;
}
//read line by line
const size_t line_size = 300;
char* line = malloc(line_size);
while (fgets(line, line_size, fh) != NULL) {
printf(line);
}
free(line); // dont forget to free heap memory
A complete, fgets() solution:
#include <stdio.h>
#include <string.h>
#define MAX_LEN 256
int main(void)
{
FILE* fp;
fp = fopen("file.txt", "r");
if (fp == NULL) {
perror("Failed: ");
return 1;
}
char buffer[MAX_LEN];
while (fgets(buffer, MAX_LEN, fp))
{
// Remove trailing newline
buffer[strcspn(buffer, "\n")] = 0;
printf("%s\n", buffer);
}
fclose(fp);
return 0;
}
Output:
First line of file
Second line of file
Third (and also last) line of file
Remember, if you want to read from Standard Input (rather than a file as in this case), then all you have to do is pass stdin as the third parameter of fgets() method, like this:
while(fgets(buffer, MAX_LEN, stdin))
Appendix
Removing trailing newline character from fgets() input
how to detect a file is opened or not in c
readLine() returns pointer to local variable, which causes undefined behaviour.
To get around you can:
Create variable in caller function and pass its address to readLine()
Allocate memory for line using malloc() - in this case line will be persistent
Use global variable, although it is generally a bad practice
Use fgets() to read a line from a file handle.
Some things wrong with the example:
you forgot to add \n to your printfs. Also error messages should go to stderr i.e. fprintf(stderr, ....
(not a biggy but) consider using fgetc() rather than getc(). getc() is a macro, fgetc() is a proper function
getc() returns an int so ch should be declared as an int. This is important since the comparison with EOF will be handled correctly. Some 8 bit character sets use 0xFF as a valid character (ISO-LATIN-1 would be an example) and EOF which is -1, will be 0xFF if assigned to a char.
There is a potential buffer overflow at the line
lineBuffer[count] = '\0';
If the line is exactly 128 characters long, count is 128 at the point that gets executed.
As others have pointed out, line is a locally declared array. You can't return a pointer to it.
strncpy(count + 1) will copy at most count + 1 characters but will terminate if it hits '\0' Because you set lineBuffer[count] to '\0' you know it will never get to count + 1. However, if it did, it would not put a terminating '\0' on, so you need to do it. You often see something like the following:
char buffer [BUFFER_SIZE];
strncpy(buffer, sourceString, BUFFER_SIZE - 1);
buffer[BUFFER_SIZE - 1] = '\0';
if you malloc() a line to return (in place of your local char array), your return type should be char* - drop the const.
Here is my several hours... Reading whole file line by line.
char * readline(FILE *fp, char *buffer)
{
int ch;
int i = 0;
size_t buff_len = 0;
buffer = malloc(buff_len + 1);
if (!buffer) return NULL; // Out of memory
while ((ch = fgetc(fp)) != '\n' && ch != EOF)
{
buff_len++;
void *tmp = realloc(buffer, buff_len + 1);
if (tmp == NULL)
{
free(buffer);
return NULL; // Out of memory
}
buffer = tmp;
buffer[i] = (char) ch;
i++;
}
buffer[i] = '\0';
// Detect end
if (ch == EOF && (i == 0 || ferror(fp)))
{
free(buffer);
return NULL;
}
return buffer;
}
void lineByline(FILE * file){
char *s;
while ((s = readline(file, 0)) != NULL)
{
puts(s);
free(s);
printf("\n");
}
}
int main()
{
char *fileName = "input-1.txt";
FILE* file = fopen(fileName, "r");
lineByline(file);
return 0;
}
const char *readLine(FILE *file, char* line) {
if (file == NULL) {
printf("Error: file pointer is null.");
exit(1);
}
int maximumLineLength = 128;
char *lineBuffer = (char *)malloc(sizeof(char) * maximumLineLength);
if (lineBuffer == NULL) {
printf("Error allocating memory for line buffer.");
exit(1);
}
char ch = getc(file);
int count = 0;
while ((ch != '\n') && (ch != EOF)) {
if (count == maximumLineLength) {
maximumLineLength += 128;
lineBuffer = realloc(lineBuffer, maximumLineLength);
if (lineBuffer == NULL) {
printf("Error reallocating space for line buffer.");
exit(1);
}
}
lineBuffer[count] = ch;
count++;
ch = getc(file);
}
lineBuffer[count] = '\0';
char line[count + 1];
strncpy(line, lineBuffer, (count + 1));
free(lineBuffer);
return line;
}
char linebuffer[256];
while (!feof(myFile)) {
const char *line = readLine(myFile, linebuffer);
printf("%s\n", line);
}
note that the 'line' variable is declared in calling function and then passed, so your readLine function fills predefined buffer and just returns it. This is the way most of C libraries work.
There are other ways, which I'm aware of:
defining the char line[] as static
(static char line[MAX_LINE_LENGTH]
-> it will hold it's value AFTER returning from the function). -> bad,
the function is not reentrant, and
race condition can occur -> if you
call it twice from two threads, it
will overwrite it's results
malloc()ing the char line[], and
freeing it in calling functions ->
too many expensive mallocs, and,
delegating the responsibility to free the buffer to another function (the most elegant solution is to call malloc and free on any buffers in same function)
btw, 'explicit' casting from char* to const char* is redundant.
btw2, there is no need to malloc() the lineBuffer, just define it char lineBuffer[128], so you don't need to free it
btw3 do not use 'dynamic sized stack arrays' (defining the array as char arrayName[some_nonconstant_variable]), if you don't exactly know what are you doing, it works only in C99.
void readLine(FILE* file, char* line, int limit)
{
int i;
int read;
read = fread(line, sizeof(char), limit, file);
line[read] = '\0';
for(i = 0; i <= read;i++)
{
if('\0' == line[i] || '\n' == line[i] || '\r' == line[i])
{
line[i] = '\0';
break;
}
}
if(i != read)
{
fseek(file, i - read + 1, SEEK_CUR);
}
}
what about this one?
Implement method to read, and get content from a file (input1.txt)
#include <stdio.h>
#include <stdlib.h>
void testGetFile() {
// open file
FILE *fp = fopen("input1.txt", "r");
size_t len = 255;
// need malloc memory for line, if not, segmentation fault error will occurred.
char *line = malloc(sizeof(char) * len);
// check if file exist (and you can open it) or not
if (fp == NULL) {
printf("can open file input1.txt!");
return;
}
while(fgets(line, len, fp) != NULL) {
printf("%s\n", line);
}
free(line);
}
Hope this help. Happy coding!
You should use the ANSI functions for reading a line, eg. fgets. After calling you need free() in calling context, eg:
...
const char *entirecontent=readLine(myFile);
puts(entirecontent);
free(entirecontent);
...
const char *readLine(FILE *file)
{
char *lineBuffer=calloc(1,1), line[128];
if ( !file || !lineBuffer )
{
fprintf(stderr,"an ErrorNo 1: ...");
exit(1);
}
for(; fgets(line,sizeof line,file) ; strcat(lineBuffer,line) )
{
if( strchr(line,'\n') ) *strchr(line,'\n')=0;
lineBuffer=realloc(lineBuffer,strlen(lineBuffer)+strlen(line)+1);
if( !lineBuffer )
{
fprintf(stderr,"an ErrorNo 2: ...");
exit(2);
}
}
return lineBuffer;
}
My implement from scratch:
FILE *pFile = fopen(your_file_path, "r");
int nbytes = 1024;
char *line = (char *) malloc(nbytes);
char *buf = (char *) malloc(nbytes);
size_t bytes_read;
int linesize = 0;
while (fgets(buf, nbytes, pFile) != NULL) {
bytes_read = strlen(buf);
// if line length larger than size of line buffer
if (linesize + bytes_read > nbytes) {
char *tmp = line;
nbytes += nbytes / 2;
line = (char *) malloc(nbytes);
memcpy(line, tmp, linesize);
free(tmp);
}
memcpy(line + linesize, buf, bytes_read);
linesize += bytes_read;
if (feof(pFile) || buf[bytes_read-1] == '\n') {
handle_line(line);
linesize = 0;
memset(line, '\0', nbytes);
}
}
free(buf);
free(line);
Provide a portable and generic getdelim function, test passed via msvc, clang, gcc.
/*
* An implementation conform IEEE Std 1003.1-2017:
* https://pubs.opengroup.org/onlinepubs/9699919799/functions/getdelim.html
*
* <nio.h>:
* https://github.com/junjiemars/c/blob/c425bd0e49df35a2649327664d3f6cd610791996/src/posix/nio.h
* <nio.c>:
* https://github.com/junjiemars/c/blob/c425bd0e49df35a2649327664d3f6cd610791996/src/posix/nio.c
*
*/
#include <errno.h>
#include <stdlib.h>
#include <stdio.h>
#include <limits.h>
/*
* LINE_MAX dependents on OS' implementations so check it first.
* https://github.com/junjiemars/c/blob/c425bd0e49df35a2649327664d3f6cd610791996/src/posix/nlim_auto_check
*/
#define NM_LINE_MAX 4096 /* Linux */
#if (MSVC)
typedef SSIZE_T ssize_t;
# if !defined(SSIZE_MAX)
# define SSIZE_MAX ((ssize_t)((size_t)((ssize_t)-1) >> 1))
# endif
#endif
ssize_t getdelim(char **restrict lineptr, size_t *restrict n, int delimiter,
FILE *restrict stream);
#if defined(getline)
# undef getline
#endif
#define getline(lp, n, f) getdelim((lp), (n), 0x0a, (f))
ssize_t
getdelim(char **restrict lineptr, size_t *restrict n, int delimiter,
FILE *restrict stream)
{
int c;
char *p, *p1;
ssize_t len;
if (NULL == lineptr || NULL == n || NULL == stream
|| (UCHAR_MAX < delimiter || delimiter < 0))
{
errno = EINVAL;
return EOF;
}
if (feof(stream) || ferror(stream))
{
return EOF;
}
if (0 == *lineptr)
{
if (0 == *n)
{
*n = NM_LINE_MAX;
}
*lineptr = malloc(*n);
if (0 == *lineptr)
{
return EOF;
}
}
p = *lineptr;
len = 0;
while (EOF != (c = fgetc(stream)))
{
if (SSIZE_MAX == (ssize_t) len)
{
errno = EOVERFLOW;
return EOF;
}
if ((size_t) len == (*n - 1))
{
*n <<= 1;
p1 = realloc(*lineptr, *n);
if (0 == p1)
{
return EOF;
}
*lineptr = p1;
p = p1 + len;
}
*p++ = (char) c;
len++;
if (c == delimiter)
{
break;
}
}
if (ferror(stream))
{
return EOF;
}
*p = 0;
return len;
}
int
main(void)
{
FILE *fp;
char *line = NULL;
size_t len = 0;
ssize_t read;
fp = fopen("/some-file", "r");
if (fp == NULL)
exit(1);
while ((read = getline(&line, &len, fp)) != -1) {
printf("Retrieved line of length %zu :\n", read);
printf("%s", line);
}
if (ferror(fp)) {
/* handle error */
}
free(line);
fclose(fp);
return 0;
}
You make the mistake of returning a pointer to an automatic variable.
The variable line is allocated in the stack and only lives as long as the function lives.
You are not allowed to return a pointer to it, because as soon as it returns the memory will be given elsewhere.
const char* func x(){
char line[100];
return (const char*) line; //illegal
}
To avoid this, you either return a pointer to memory which resides on the heap eg. lineBuffer
and it should be the user's responsibility to call free() when he is done with it.
Alternatively you can ask the user to pass you as an argument a memory address on which to write the line contents at.
I want a code from ground 0 so i did this to read the content of dictionary's word line by line.
char temp_str[20]; // you can change the buffer size according to your requirements And A single line's length in a File.
Note I've initialized the buffer With Null character each time I read line.This function can be Automated But Since I need A proof of Concept and want to design a programme Byte By Byte
#include<stdio.h>
int main()
{
int i;
char temp_ch;
FILE *fp=fopen("data.txt","r");
while(temp_ch!=EOF)
{
i=0;
char temp_str[20]={'\0','\0','\0','\0','\0','\0','\0','\0','\0','\0','\0','\0','\0','\0','\0','\0','\0','\0','\0'};
while(temp_ch!='\n')
{
temp_ch=fgetc(fp);
temp_str[i]=temp_ch;
i++;
}
if(temp_ch=='\n')
{
temp_ch=fgetc(fp);
temp_str[i]=temp_ch;
}
printf("%s",temp_str);
}
return 0;
}
So i have to write a function that reads a file (.txt) and searches for a specific string, and then make it return the whole line that the string was on.
For example, one line is composed by student number, name, date of birth, address and course. I need to search for a name, and i need it to return the whole line, containing number, name, etc.
Ex :
Input : Search for student name : HUGO
Output :
61892 HUGOABC 12-02-2001 Address123 ETD
81029 HUGOBCA 09-09-2000 Address123 EAC
Here's my code :
fp = fopen("database_Alunos.txt", "r+");
if (fp == NULL) {
printf("Error! File is NULL...");
system("pause");
main();
}
else {
char nome[50];
printf("Choose name to search : ");
scanf("%[^\n]s", &nome);
/* ??? */
fclose(fp);
system("pause");
main();
fp is a FILE *fp, declared on top of main();
I need to know what kind of functions I can use in the space in the code with the question marks to make it scan for 'nome' and return the whole line
You'll need to loop through a getline using your fp, then you can use for example strstr to check if the name is present in this string. Note that you'll have to handle the case when the name is present in the address.
char *line = NULL;
size_t len = 0;
ssize_t read;
while ((read = getline(&line, &len, fp)) != -1) {
if (strstr(line, nome) != NULL) {
printf("%s\n", line);
}
}
Ok i figured it out, this is a function to read the line
int readline(char *buff, int len, FILE *fp) {
buff[0] = '\0';
buff[len - 1] = '\0';
char *tmp;
if (fgets(buff, len, fp) == NULL) {
*buff = '\0';
return 0;
}
else {
if ((tmp = strrchr(buff, '\n')) != NULL) {
*tmp = '\0';
}
}
return 1;
}
Func to read name and return lines :
scanf("%[^\n]s", fgets(nome, sizeof(nome), stdin));
char line[1024];
while (readline(line, 1024, fp)) {
char *aux = strdup(line);
char *numero = strtok(aux, "\t");
char *nomeAluno = strtok(NULL, "\t");
if (strstr(nomeAluno, nome) != NULL) {
printf("%s\n", line);
}
}
}
** Updated 26/10 -> First of all thank you all for you help, I am getting closer now, I need more work and studying but I really appreciate you are helping me a lot :-)
Still don't know why the first "rain" word in the input.txt file is not getting the positive output from strcmp, and from the cmd I can see the "<" bracket don't appear except for the LAST line which is the line that works.
Also checked the highlighted response from Removing trailing newline character from fgets() input
and even if I change the code to the following:
while( fgets (line, sizeof line, fp)!=NULL ) {
/* remove \n from at the end of the str buffer*/
char * pos;
/*
if ((pos = strchr(line, '\n')) != NULL)
*pos = '\0';
*/
line[strcspn(line, "\n")] = 0;
I get the same result as if I use the if block instead. Maybe I'm getting extra \0 which might be the case. Anyone has a link where I can read about the delimiters I just used, or a nice reference of a debugger, etc. ... which I will have a look as soon as I come here? Thank you so much in advance!
read5.c version: Now from that input.txt file, it had an extra space on the last "rain" word, I removed the space, and it was able to find and get that last word compare as a true result, running in the strcmp if block. but that was the only string that was a true positive result from that if block.
on the cmd I can see:
$./read5 input.txt rain output.txt sun
>Maria
>rain
>manel
>Bla bla
<rain>
Found it! rain
On the output.txt it becomes:
Maria
rain
manel
Bla bla
sun
read5.c
#include <stdio.h>
#include <string.h>
/**
* Compile program:
* gcc read3.c -o read3
*
*/
int main (int argc, char **argv) {
FILE *fp, *fo;
char *compare, *replace;
char line[246];
if (argc <= 4){
printf(">Missing arguments on the command line.\n");
printf(">Be sure you run the program as\n\"./read3 input.txt compare outout.txt replace\"\n\n");
}
/* opening file for reading */
fp = fopen(argv[1] , "r");
if(fp == NULL){
perror("Error opening input file");
return 1;
}
compare = argv[2];
fo = fopen(argv[3], "w");
if(fo == NULL){
perror("Error opening output file");
return 1; //TODO check if: return 1 because it was expected, right?
}
replace = argv[4];
/*
printf(); made to test version 2
//printf("We are going to compare %s\n", compare);
//printf("We are going to replace it with %s\n", replace);
*/
while( fgets (line, sizeof line, fp)!=NULL ) {
/* remove \n from at the end of the str buffer*/
char * pos;
if ((pos = strchr(line, '\n')) != NULL)
*pos = '\0';
/* print str enclosed in <> so we can see what str actually contains */
//printf("Inside the loop, got the string: %s\n", line);
//printing the strings with defined delimiters
printf("<%s>\n", line);
if(strcmp(compare, line) == 0){
printf("Found it! %s \n", line);
fprintf(fo, "%s\n", replace);
}
else{
fprintf(fo, "%s\n", line);
}
}
fclose(fp);
fclose(fo);
return 0;
}
First question with no edits: 25/10
I need to make a program that is run like this:
./read2 input.txt rain output.txt sun
It reads the input.txt, searches for rain string and if finds it, replaces it with sun string and outputs all the text from input.txt with the replacements to the output.txt.
But with the code that I have so far, the strcmp is not comparing the strings I want, maybe it has the extra space that I get on the command line, I don't know... for now what is doing is copying everything from input.txt to output.txt... It's running the else block always...
Read2.c:
#include <stdio.h>
#include <string.h>
int main(int argc, char **argv) {
FILE *fp, *fo;
char str[60];
//char* token;
/* opening file for reading */
fp = fopen(argv[1], "r");
char *compare = argv[2];
fo = fopen(argv[3], "w+");
char *replace = argv[4];
if (fp == NULL) {
perror("Error opening file");
return(-1);
}
//printf("We are going to compare %s\n", compare);
//printf("We are going to replace it with %s\n", replace);
while (fgets(str, 60, fp) != NULL) {
/* writing content to stdout */
//Take the \n out
//token = strtok(str, "\n");
printf("Inside the loop, got the string: %s\n", str);
if (strcmp(compare, str) == 0) {
//puts(str);
printf("Found it! %s \n", str);
fprintf(fo, "%s", replace);
} else {
fprintf(fo, "%s", str);
}
}
fclose(fp);
return(0);
}
input.txt:
Maria
rain
manel
Bla bla
rain
Ouput.txt becomes exactly as input.txt and before it was empty, so the code is working, except the if block that tests with strcmp.
The problem is the \n at the end of the str buffer. fgets adds the \n at end end of the line it reads, you need to get rid of it before comparing.
This is what you need:
while (fgets(str, 60, fp) != NULL) {
/* remove \n from at the end of the str buffer*/
char *pos;
if ((pos = strchr(str, '\n')) != NULL)
*pos = '\0';
/* print str enclosed in <> so we can see what str actually contains */
printf("Inside the loop, got the string: <%s>\n", str);
if (strcmp(compare, str) == 0) {
printf("Found it! %s\n", str);
fprintf(fo, "%s\n", replace);
}
else {
fprintf(fo, "%s\n", str);
}
}
Look at the comments in the code for explanations.
read.c
#include <stdio.h>
#include <string.h>
/**
* How to compile program:
* gcc read.c -o read
*
* How to run the program:
* .> ./read input.txt rainy output.txt sunny
* (On Windows MinGW compiler, simply:
* .> read input.txt rainy output.txt sunny - without ./)
*
*/
int main (int argc, char **argv) {
FILE *fp, *fo;
char *compare, *replace;
char line[246];
if (argc <= 4){
printf(">Missing arguments on the command line.\n");
printf(">Be sure you run the program as\n\"./read input.txt compare outout.txt replace\"\n\n");
}
/* Opening files for reading */
fp = fopen(argv[1] , "r");
if(fp == NULL){
perror("Error opening input file");
return 1;
}
compare = argv[2];
fo = fopen(argv[3], "w");
if(fo == NULL){
perror("Error opening output file");
return 1;
}
replace = argv[4];
while( fgets (line, (sizeof line), fp)!=NULL ) {
line[strcspn(line, "\n")] = 0;
if(strcmp(compare, line) == 0){
printf("Found it! %s \n", line);
fprintf(fo, "%s\n", replace);
}
else{
fprintf(fo, "%s\n", line);
}
}
fclose(fp);
fclose(fo);
return 0;
}
/*
Important info
strcspn ::
Locate first occurrence of character in string,
after locating the first occurrence of \n, replaces it by 0.
Sources::
https://stackoverflow.com/questions/2693776/removing-trailing-newline-character-from-fgets-input/28462221#28462221
Used to debug:
.>printf("1st: Reads input.txt, removes '\\n' from fgets, and prints it \n");
.>printf("2nd: Compares each line with 'rainy' \n");
.>printf("<%s>\n", line);
*/
input.txt
cloudy
rainy
chilly
rainy
rainy
Your approach fails because the lines read from the input file contain a trailing newline '\n' that makes the comparison return non zero.
You can strip the newline before comparing with the search string.
Note that there are other problems:
you should verify that enough command line arguments have been passed by testing argc > 4.
there is no need to open the output file in update mode "w+", "w" is simpler and better.
60 bytes is a bit small for the line array, limiting the longest line handled correctly to 58 bytes.
Here is an improved version:
#include <stdio.h>
#include <string.h>
int main(int argc, char **argv) {
FILE *fp, *fo;
char *compare, *replace;
char line[256];
if (argc <= 4) {
printf("missing command line arguments\n");
return 1;
}
fp = fopen(argv[1], "r");
if (fp == NULL) {
perror("Error opening input file");
return 1;
}
compare = argv[2];
fo = fopen(argv[3], "w");
if (fo == NULL) {
perror("Error opening output file");
return 1;
}
replace = argv[4];
while (fgets(line, sizeof line, fp) != NULL) {
line[strcspn(line, "\n")] = '\0';
if (strcmp(line, compare) == 0) {
printf("fount it!);
fprintf(fo, "%s\n", replace);
} else {
fprintf(fo, "%s\n", line);
}
}
fclose(fp);
fclose(fo);
return 0;
}
Note that long lines will be broken into chunks that fit in the line array, so there may be false positives with the above naive approach.
You can remove this limitation completely with this inner loop:
int c;
int pos = 0;
int cmplen = strlen(compare);
for (;;) {
c = getc(fp);
if (c == '\n' || c == EOF) {
if (pos == cmplen) {
fprintf(fo, "%s", replace);
} else
if (pos > 0) {
fprintf(fo, "%*s", pos, compare);
}
pos = 0;
if (c == EOF)
break;
} else {
if (pos >= 0) {
if (compare[pos] == (char)c) {
pos++;
continue;
}
if (pos > 0) {
fprintf(fo, "%*s", pos, compare);
}
pos = -1;
}
}
putc(c, fo);
}
I need help with this little program I am trying to make.
There is .txt file:
namas house
katinas cat
suo dog
skaicius number
I want to find a line which begins with specific word and then prints second word of that line.
For example, user enters word katinas. Program looks through file, finds line that begins with katinas and finally prints.
What I have so far:
int main()
{
char word;
printf("Enter your word: ");
scanf("%s", &word);
FILE *fp;
fp = fopen("data.txt", "r+");
char buffer[256];
while (fgets(buffer, sizeof buffer, fp) != NULL && atoi(buffer) != word)
;
if (feof(fp))
{
printf(&buffer);
}
fclose(fp);
return 0;
}
Thank you.
There were several mistakes in the code as pointed out elsewhere. This answer will find whole words so for example "suo" but not "su".
#include<stdio.h>
#include<string.h>
int main()
{
char word[256]; // adequate string space (not single char)
char buffer[256];
char *sptr;
FILE *fp;
int found = 0;
printf("Enter your word: ");
scanf("%s", word); // requires a string pointer (note no &)
fp = fopen("data.txt", "r"); // removed "+"
if (fp) {
while (fgets(buffer, sizeof buffer, fp) != NULL) {
sptr = strtok(buffer, " \t\r\n");
if (sptr && strcmp(sptr, word) == 0) {
sptr = strtok(NULL, " \t\r\n");
if (sptr) {
printf("%s\n", sptr);
found = 1;
break;
}
}
}
fclose(fp);
}
if (!found)
printf ("%s not found\n", word);
return 0;
}
You could use a simple logic, just like using a 'for' to search for the word and right after you find the specific word that you want, continue with the 'for' until find a blank space (use ' ' to determinete the end and the beginning of a word) then print out all the letters until find the next blank ' '. This should work just fine.
char word; is a single char which can't store lines; should be an array in order to read a line.
atoi(buffer) != word you are comparing an int (returned by atoi()) with a pointer(array name gets converted into a pointer here). I really don't see the purpose of this.
You don't need to check if end of file has been reached. You just loop through the file line-by-line and check for your string.
Calling printf without format specifier is not safe and you are also passing char (*)[256] whereas printf expects a const char*.
You should also error checking on fopen().
Use a standard prototype for main() such as: int main(void)
After correcting all these, the code would be simplified to:
#include<stdio.h>
#include<string.h>
int main(void)
{
char word[256] = {0};
char buffer[256] = {0};
FILE *fp;
printf("Enter your word: ");
scanf("%s", word);
fp = fopen("data.txt", "r+");
if (!fp) { /* error */}
while ( fgets(buffer, sizeof buffer, fp) )
{
if( strstr(buffer, word) == buffer )
printf("Found: %s\n", buffer);
}
return 0;
}
There's no library function to find if a string "starts with" in C. I am using strstr to achieve that. If there's a match and it's equal to the starting address of the buffer, then it starts with word. Because strstr returns to a pointer to the first match.
#include <stdio.h>
int main(void){
char buffer[256];
char word[256], second_word[256];
char format[256];
FILE *fp;
printf("Enter your word: ");
scanf("%255[A-Za-z]", word);
sprintf(format, "%s %%255s", word);
fp = fopen("data.txt", "r");
while (fgets(buffer, sizeof buffer, fp) != NULL) {
if (sscanf(buffer, format, second_word) == 1) {
printf("%s\n", second_word);
break;//continue;?
}
}
fclose(fp);
return 0;
}
here's the code in question:
FILE *fp;
char str[256];
/* opening file for reading */
fp = fopen("file.txt" , "r");
if(fp == NULL) {
perror("Error opening file");
return(-1);
}
while( fgets (str, sizeof(str), fp)) {
int i;
char *temp;
temp=malloc(257);
for(i=0;i<sizeof(str)-1;i++){
if(isalpha(str[i])){
append(temp,str[i]);
}else{
printf(" %s ",temp);
temp=calloc(257,sizeof(char));
}
}
}
if the text file is the following:
"Here's a text
file example. No
idea what's wrong."
then it will output the following:
"Here s a text vf file example No vf idea what s wrong".
Desired output for reference:
"Here s a text file example No idea what s wrong"
Basically some weird stuff every time there's a newline involved. Could be "vf" when i run it. Could be "ZG" the next time. It changes every time i run the program.
Reading parts of buf not filled by fgets()`.
Replace
// for(i=0;i<sizeof(str)-1;i++)
for(i=0;i<strlen(str);i++)
or better
// for(i=0;i<sizeof(str)-1;i++)
size_t len = strlen(str);
// removed potenital ending '\n'
if ((len > 0) && (str[len-1] == '\n')) len--;
size_t i;
for (i = 0; i < len; i++)
Perhaps I didn't understand what you're doing but if you just want to read the whole file in one string you can do something like this
int main(int argc, const char * argv[])
{
FILE *fp;
char str[256];
char *temp = calloc(257, 1);
fp = fopen("file.txt" , "r");
if(fp == NULL) {
perror("Error opening file");
return(-1);
}
while( fgets (str, sizeof(str), fp)) {
int i;
//char *temp;
if (str[strlen(str)-1] == '\n') {
str[strlen(str)-1] = ' ';
}
strncat(temp, str, 257);
}
puts(temp);
}
There is no problem with fgets. It automatically appends terminating null character.
Also you do not free memory before allocating new. It's not good.
#include <stdio.h>
#include <stdlib.h>
int main()
{
FILE *fp;
char str[256];
/* opening file for reading */
fp = fopen("file.txt" , "r");
if(fp == NULL) {
perror("Error opening file");
return(-1);
}
while( fgets (str, sizeof(str), fp)) {
int i;
char temp[256]; //buffer; can allocate on the stack, no need for malloc
char *temp1; //pointer at the beginning of the buffer (used to do my own append())
temp1=temp; //for my own appending
for(i=0;i<sizeof(str);i++){
int ch=str[i]; //alias the str[i]
if(isalpha(ch)||ch=='"'){ //let these chars thru
*temp1++=ch; //my own append()
}else if(ch=='\0'){//already at the end of buffer, end loop and print
*temp1=ch; //don't forget to end the string with '\0' (for printing functions)
break;
}else if(ch=='.'){ // you seem to want to skip dots
continue;
}
else {
*temp1++=' '; //replace other nonalpha characters with ' '
}
}
printf("%s",temp);
}
}