There are multiple .txt files in a folder like;
math.txt
physics.txt
programming.txt
User must enter lesson's name and then program should open .txt file and read it.
The problem is I can't use a variable in fopen() function.
FILE *lesson= fopen("...\\lessons\\[user input].txt","r");
any idea?
What makes you think you can't use a variable in fopen()?
Try this:
#define PATH_STRING "...\\lessons"
//Allocate enough memory for the whole filepath
char *buffer = malloc(strlen(PATH_STRING) + strlen(argv[index]) + 6);
//Write the path into the buffer
sprintf(buffer,"%s\\%s.txt", PATH_STRING, argv[index]);
//Pass the pointer to the buffer as an argument of fopen()
FILE *fp = fopen(buffer,"r");
free(buffer);
Related
I need to read a text file with 7 lines into 7 different variables. The text file looks like this:
.2661
A.txt
B.txt
C.txt
1
2
0.5 0.6
These are the variables that I need to store each line into:
float value1; // line 1 from .txt file
char *AFileName; // line 2 from .txt file
char *BFileName; // line 3 from .txt file
char *CFileName; // line 4 from .txt file
int value2; // line 5 from .txt file
int lastLineLength; // line 6 from .txt file
double lastLine[lastLineLength]; // line 7 from .txt file - this can be different lengths
I have currently been doing this by just using the arguments when I call my program from the command line and the argv command.
First open the file using fopen with read access:
FILE *inputFile = fopen(filename, "r");
if(!inputFile) {
// Error opening file, handle it appropriately.
}
Then read the data from the file using fscanf. The first parameter is the FILE * we created above. The second parameter is a format string that specifies what fscanf should expect while reading the file. The remaining parameters are pointers to variables that will hold the data read from the file.
int variablesFound;
variablesFound = fscanf(inputFile, "%f\n%s\n%s\n%s\n%d\n%d\n", &value1, AFileName, BFileName, CFileName, &value2, &lastLineLength);
if(variablesFound < 6) {
// There was an error matching the file contents with the expected pattern, handle appropriately.
}
double lastLine[lastLineLength];
// Iterate over the last line.
int lastLineIndex;
for(lastLineIndex = 0; lastLineIndex < lastLineLength; lastLineIndex++) {
fscanf(inputFile, "%lf", &lastLine[lastLineIndex]);
fscanf(inputFile, " "); // Eat the space after the double.
}
Edit
After comments I realized it might be worth noting that you have to allocate memory to your variables as the real first step. The primitives (those with an & below) can be declared as normal. For the string (char array), you'll want to do one of the following:
char *aFileName = calloc(MAX_FILENAME_SIZE + 1, sizeof(char));
or
char aFileName[MAX_FILENAME_SIZE + 1];
Depending on what your purpose with aFileName would be determines which method would be appropriate. However, assuming this code appears in the main or doesn't need to exist beyond the scope of the function, the latter would be better as it doesn't require free()ing the variable after you're done with it.
It also may be worth while singling out the code that deals with reading input if your requirements change often.
You can read from the file as follows:
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
FILE * fp;
char * line = NULL;
size_t len = 80;
fp = fopen("<path to your file>", "r");
if (fp == NULL)
exit(-1);
while (getline(&line, &len, fp) != -1)
printf("%s", line);
fclose(fp);
return 0;
}
getline reads character strings from the file, so you'd have to parse the lines as needed (atoi, atof).
I want to open a file. Easy enough. Use fopen(). However, what file to open depends on the user input. I am somewhat proficient in Korn Shell scripting and this is easily done using variable substitution: $(var). I am unable to figure out the correct format in C. Could someone please give me some insight?
My code -
#include <stdlib.h>
#include <stdio.h>
char statsA[100];
char fileA[50];
int main (void)
{
printf("Enter file to open\n");
gets(fileA);
FILE *statsA;
statsA = fopen("c:/Users/SeanA/C/***<fileA>***", "r+");
.......................................^ What goes here?
I am unsure of how to include the user input in the fopen string.
This is what sprintf is for. It works like printf, except that its output goes to a string instead of stdout.
char filename[100];
sprintf(filename, "c:/Users/SeanA/C/%s", fileA);
statsA = fopen(filename, "r+");
Also, the definition of statsA you have inside of main masks the definition at file scope. You probably want to give these different names.
You must concatenate both strings manually. Something like this
char* folder = "c:/Users/SeanA/C/";
char* path = malloc(strlen(fileA) + strlen(folder) + 1);
path = strcpy(folder);
path = strcat(fileA);
FILE *statsA = fopen(path, "r+");
free(path);//Always free your memory
Do scanf to get the file from the user.
make a char array to hold the filename.
char filename[15];
Now ask for the file name:
printf("What is the name of the file?\n");
scanf("%s", &filename);
Note: Include the FULL file name. so if I have a text doc called filename The user would need to type filename.txt
Now you have the file name you can declare a file pointer
FILE * fp;
fp = fopen(filename, "r");
Now you should be able to scan your file!
fscanf(fp, "%d", &value);
EDIT: I did not notice you wanted string concatenation with your file path.
Since you know the predefined path you can make another char array that holds that string path
char fullPath[100];
char path[75] = "c:/Users/SeanA/C/";
Now you can use strcat to bring them all together!
strcat(fullPath, path);
strcat(fullPath, filename);
Now you do fopen(fullPath, "r");
Edit: Deleted all but the main question.
My program here is supposed to create a file at a specified directory, and write specified text to it. A correct file's path and content should look something like this:
Path: D:\test.txt
Content: The printing succeeded.
For some reason, my code won't recognize the "path" variable. I don't know what I'm doing wrong here. The "text" variable works fine.
#include<stdio.h>
int main()
{
//Declaring variables
char path[999];
char text[999];
FILE *fp;
//prompting for path variable
printf("Specify a file path.\n");
fgets(path,999,stdin);
printf(path);
//prompting for the text variable.
printf("What do you want to write?");
fgets(text,999,stdin);
printf(text);
//opening and printing to file.
//fp = fopen("D:\\test.txt", "w");
fp = fopen(path, "w");
fprintf(fp, text);
fclose(fp);
//test print to see that the program completed correctly.
printf("\nThe printing has been done.");
return 0;
}
The thing I don't understand is that fp = fopen("D:\\test.txt", "w"); works, but fp = fopen(path, "w"); doesn't. I've tried putting in these different paths.:
D:\\test.txt
D:\test.txt
D\test.txt
D\\test.txt
It doesn't open the file when you open the variable path because fgets() reads the newline and puts it at the end of the string (if there's enough space in the buffer). In order to make it work you have to manually remove the newline from the string.
Try this before opening the file.
if(isspace(path[strlen(path)-1]))
path[strlen(path)-1]='\0';
You might also need to include <ctype.h>
I am trying to read in a file and it tells me it cant find the file. I built i have a built in checker that looks to see if the file is there. I have the data file in my debug folder. Am I reading the file incorrectly? I am also using codeblocks for the IDE.
Here is my function calling my file:
char fileData[3];
int bound = 96;
//file pointer and file info
FILE *ips;
ips = fopen("data.txt", "r");
if (ips == NULL)
printf("Please check file!\n"); //this is the output I get
else {
//for loop to scan through file, and retrive the letters
int i;
for(i=0; i<bound; i++)
fscanf(ips, "%c", &fileData);
addBoggleData(head1, fileData);
}
//closes the file system
close(ips);
}
you stated the file failed to open.
Since the fopen() file name parameter has no path info.
and you stated the file is in the debug directory.
1) the execution and the file must be in the same directory
2) in this case, both the executable and the data file must be in the debug directory.
You are passing the wrong parameter to fscanf(), you should pass the address of the ith element, like this
fscanf(ips, "%c", &fileData[i]);
and to be able to tell whether the data was read succesfully, you must check the return value of fscanf(), like
if (fscanf(ips, "%c", &fileData[i]) != 1)
{
warningReadingFailure();
}
Also, the fileData array is way too small, you need to make it at least as big, as the number of bytes you intend to read from the file, i.e.
int bound = 96;
char fileData[bound];
to read/write a file i need file pointer in language C in Unix environment.
I know a file name and path, but how to get file pointer using its name and path.
#include <stdio.h>
FILE * pFile;
pFile = fopen ("myfile.txt","w");
Import the standard input/output header like so
#include <stdio.h>
And then create a pointer for the file you want to open.
FILE * file_pointer;
file_pointer = fopen ("[path to file]","w");
fclose(file_pointer);
NOTE: Specify whole path to file if it is not in the same directory as your source file.
Dont forget to close the file after you have done the operations you need
According to the post from ssmithstone:
#include <stdio.h>
FILE * pFile;
/* open file and check if was successful */
if ((pFile = fopen("myfile.txt", "w")) == NULL)
{
/* couldn't open file; do some error handling if u want */
}
else
{
/* do s.th. */
/* close file */
fclose(pFile);
}
In this case w means writing. For other options check the link posted by Yu Hao.
Seems like you are new in C programming, I've written a C program for you, you can analyse it and I believe it will be definitely helpful to you.
#define size 50
#include <stdio.h>
int main()
{
char name[size];
FILE *file;
file = fopen("your_file.txt","w");
printf("Please enter your first name\n");
scanf("%s",name);
fprintf(file,"%s",name);
fclose(file);
return 0;
}
Details:
In line 7 the second parameter w is used as file open mode - with write privileges.
The file pointer is used to create / open a file with name "your_file.txt".
function fprintf() is same as printf() function but it writes not on console but to your file.
finally we need to close the file writing operations thus we use fclose() function
Update:
To specify your path you can write your file path with your filename.fileextension
for example: You can write it as
file = fopen("/home/depthgr8/Desktop/your_file.txt","w");
This will create your_file.txt in given path if your path exists otherwise it will throw a runtime exception - segmentation fault (core dumped)