Clear Data Inside Text File in C++

How do I clear the whole contents of a file in C?

As @stefan said using fopen() with "w" mode will do the job for you. When you open a file with "w" flag it creates an empty file for writing. If a file with the same name already exists its contents are erased and the file is treated as an empty new file.

If the file is already open you can use freopen() function from stdio.h with "w" mode as it will first close the file and then reopen it for writing erasing whatever was in the file previously.

C language ~ data file by using delete function modify text file content (File IO)

Try this

int delete_line, temp;
char reply;

printf("Enter file name: ");
scanf("%s", filename);

do{
    temp = 1;
    ....

I hope this helps.

How to remove a word from text file in C program?

This example worked for phrases, I didn't check for larger files or with more content.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void remove_word(char * text, char * word);

int main()
{
    char * filename     = "test.txt";
    char * text         = (char*)malloc(sizeof(char) * 100);
    char * wordToRemove = (char*)malloc(sizeof(char) * 20);
    // Word to remove
    strcpy(wordToRemove, "Bye"); 
    
    // Open for both reading and writing in binary mode - if exists overwritten
    FILE *fp = fopen(filename, "wb+");
    if (fp == NULL) {
        printf("Error opening the file %s", filename);
        return -1;
    }
    // Read the file
    fread(text, sizeof(char), 100, fp);
    printf ("Readed text: '%s'\n", text);

    // Call the function to remove the word
    remove_word(text, wordToRemove);
    printf ("New text: '%s'\n", text);

    // Write the new text
    fprintf(fp, text);
    fclose(fp);

    return 0;
}

void remove_word(char * text, char * word)
{
    int sizeText = strlen(text);
    int sizeWord = strlen(word);
    
    // Pointer to beginning of the word
    char * ptr = strstr(text, word);
    if(ptr)
    {
        //The position of the original text
        int pos = (ptr - text);

        // Increment the pointer to go in the end of the word to remove
        ptr = ptr + sizeWord;                
        
        // Search in the phrase and copy char per char
        int i;
        for(i = 0; i < strlen(ptr); i++)
        {
            text[pos + i] = ptr[i]; 
        }
        // Set the "new end" of the text               
        text[pos + i] = 0x00;      
    }   
}

Clear data inside all files in C++

fstream can't open all files of a directory, instead, you can iterate each file.

This example only works on C++17

    #include <string>
    #include <iostream>
    #include <filesystem>
    #include <fstream>
    //namespace fs = std::experimental::filesystem; //for visual studio
    namespace fs = std:::filesystem;
    int main()
    {
        std::string path = "path_to_directory";
        for (auto & p : fs::directory_iterator(path)) {
            if (fs::is_regular_file(p)){
                std::fstream fstr;
                fstr.open(p.path().c_str(), std::ios::out | std::ios::trunc);
                //do something
                fstr.close()
            }
        }
    }

Older compilers(Windows):

#include <Windows.h>
#include <string>
#include <fstream>

std::wstring path = L"path_to_directory";

path += L"\\*";
WIN32_FIND_DATA data;
HANDLE hFind;
if ((hFind = FindFirstFile(path.c_str(), &data)) != INVALID_HANDLE_VALUE) {
    do {
        if (data.dwFileAttributes & FILE_ATTRIBUTE_ARCHIVE) {
            std::fstream fstr;
            fstr.open(data.cFileName, std::ios::out | std::ios::trunc);
            //do something
            fstr.close();
        }
    } while (FindNextFile(hFind, &data) != 0);
    FindClose(hFind);
}

File Handling in C - Removing specific words from a list in text file

• You open two files: the one you've got (for reading) and a new one (for
  writing).
• You loop through the first file reading each line in turn.
• You compare the contents of each line with the words you need to
  delete.
• If the line does not match any of the deletion words, then
  you write it to the new file.

If the manipulation that you need to do is much more complex then you can literally "read it into memory" using mmap(), but that is a more advanced technique; you need to treat the file as a byte array with no zero terminator and there are lots of ways to mess that up.

How can I delete from a text file?

• You open two files: the one you've got (for reading) and a new one (for writing).
• You loop through the first file reading each line in turn.
• You compare the contents of each line with the words you need to delete.
• If the line does not match any of the deletion words, then you write it to the new file.

Josuel, as taken from my previously answered question by Richard Urwin

You can use the following code:

#include <stdio.h>

    int main()
    {
        FILE *fileptr1, *fileptr2;
        char filename[40];
        char ch;
        int delete_line, temp = 1;

        printf("Enter file name: ");
        scanf("%s", filename);
        //open file in read mode
        fileptr1 = fopen("c:\\CTEMP\\Dictionary.txt", "r");
        ch = getc(fileptr1);
        while (ch != EOF)
        {
            printf("%c", ch);
            ch = getc(fileptr1);
        }
        //rewind
        rewind(fileptr1);
        printf(" \n Enter line number of the line to be deleted:");
        scanf("%d", &delete_line);
        //open new file in write mode
        fileptr2 = fopen("replica.c", "w");
        ch = getc(fileptr1);
        while (ch != EOF)
        {
            ch = getc(fileptr1);
            if (ch == '\n')
            {
                temp++;
            }
            //except the line to be deleted
            if (temp != delete_line)
            {
                //copy all lines in file replica.c
                putc(ch, fileptr2);
            }
        }
        fclose(fileptr1);
        fclose(fileptr2);
        remove("c:\\CTEMP\\Dictionary.txt");
        //rename the file replica.c to original name
        rename("replica.c", "c:\\CTEMP\\Dictionary.txt");
        printf("\n The contents of file after being modified are as follows:\n");
        fileptr1 = fopen("c:\\CTEMP\\Dictionary.txt", "r");
        ch = getc(fileptr1);
        while (ch != EOF)
        {
            printf("%c", ch);
            ch = getc(fileptr1);
        }
        fclose(fileptr1);
        scanf_s("%d");
        return 0;

    }

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