File Copy problem

This is a discussion on File Copy problem within the C Programming forums, part of the General Programming Boards category; As part of an assignment we were given code to copy a text input file into an output file. Parts ...

  1. #1
    Registered User
    Join Date
    Feb 2010
    Posts
    1

    File Copy problem

    As part of an assignment we were given code to copy a text input file into an output file. Parts of it were missing and I think I'm really close to solving the problem, but I seem to have run into an issue where either words or missing or it prints double versions into the output file which are missing a few letters.

    I suspect it might have to do with it reading from the pipe incorrectly or that I open or closed the pipe in the wrong places but I can't seem to nail it down.

    Here's my code:
    Code:
    #include <sys/types.h>
    #include <stdio.h>
    #include <string.h>
    #include <unistd.h>
    
    #define BUFFER_SIZE 80
    #define READ_END 0
    #define WRITE_END 1
    
    int main(int argc, char *argv[]) {
        
       /* argc must be 3 to ensure the correct usage */
      if (argc != 3) {
        printf("The usage of this program is:\n");
        printf("FileCopy input.txt copy.txt\n");
        return 1;
      }
    
      else {
        /* initialize the pipe and fork variables */
        int fd[2];
        pid_t pid;
    
        /* argv[0] is the program name, argv[1] and argv[2] are the file names */
        char *infile = argv[1];
        char *outfile = argv[2];
    
        /* create a pipe */
        if (pipe(fd) == -1) {
          fprintf(stderr, "Pipe failed");
          return 1;
        }
        
        /* fork */
        pid = fork();
    
        /* if pid < 0 there is an error */
        if (pid < 0) {
          fprintf(stderr, "Fork error");
          return 1;
        }
     
        /* parent code */
        if (pid > 0) {
    
          /* close the unused end of the pipe */
          close(fd[READ_END]);
    
          /* make a buffer to store input file information */
          //char buffer[BUFFER_SIZE];
    
          /* open input file */
          FILE *in;
          in = fopen(infile, "r");
    
          /* make sure it's not null */
          if (in == NULL) {
            fprintf(stderr, "Error opening file %s\n", infile);
            return 1;
          }
          
          /* read from the file into the pipe thru the buffer */
          while (! feof(in)) {
            char buffer[BUFFER_SIZE];
            fgets(buffer, BUFFER_SIZE, in);
            write(fd[WRITE_END], buffer, strlen(buffer)+1);
          }
    
          /* close the input file */
          fclose(in);
     
          /* close the pipe */
          close(fd[WRITE_END]);
        }
    
        /* child process has pid == 0 */
        else {
    
          /* create a buffer to read from the pipe and store into the out file */
          //char buffer[BUFFER_SIZE];
    
          /* close the unused end of the pipe */
          close(fd[WRITE_END]);
    
          /* initialize the output file */
          FILE *out;
    
          /* w+ means open a file for writing and create it if it doesn't exist */
          out = fopen(outfile, "w+");
    
          /* read from the pipe to the buffer */
          //read(fd[READ_END], buffer, BUFFER_SIZE);
    
          /* write from the buffer to the file */
          //fprintf(out, "%s", buffer);
    
          while(1) {
            char buffer[BUFFER_SIZE];
            if (read(fd[READ_END], buffer, BUFFER_SIZE) != 0)
              fprintf(out,"%s",buffer);
            else
              break;
          }
            
    
          /* close the file and the pipe */
          fclose(out);
          close(fd[READ_END]);
        }
      }
    }
    Any assistance would be greatly appreciated I get the feeling at this point it's a minor mistake but I've been staring at it for hours.
    Last edited by Salem; 02-18-2010 at 09:45 AM. Reason: Added code tags - learn to use them yourself!

  2. #2
    Registered User ungalnanban's Avatar
    Join Date
    Feb 2010
    Location
    Chenai
    Posts
    12

    Thumbs up file copy

    Dear Friend,

    May be your file is not flushed, use the fflush(in),

    I used "fprintf" instead of "write " function the file content is cpoied in to the second file.

    sample code:
    Code:
    fprintf(in,"%s",buffer);
    The main error is file is not flush you can try with the above line instead of write function.
    write function also do this.

    your didn't open the out file. I solved the problem see the following code.
    Code:
    #include <sys/types.h>
    #include <stdio.h>
    #include <string.h>
    #include <unistd.h>
    
    #define BUFFER_SIZE 80
    #define READ_END 0
    #define WRITE_END 1
    
    int main(int argc, char *argv[]) {
    
    /* argc must be 3 to ensure the correct usage */
    if (argc != 3) {
    printf("The usage of this program is:\n");
    printf("FileCopy input.txt copy.txt\n");
    return 1;
    }
    
    else {
    /* initialize the pipe and fork variables */
    int fd[2];
    pid_t pid;
    
    /* argv[0] is the program name, argv[1] and argv[2] are the file names */
    char *infile = argv[1];
    char *outfile = argv[2];
    
    /* create a pipe */
    if (pipe(fd) == -1) {
    fprintf(stderr, "Pipe failed");
    return 1;
    }
    
    /* fork */
    pid = fork();
    
    /* if pid < 0 there is an error */
    if (pid < 0) {
    fprintf(stderr, "Fork error");
    return 1;
    }
    
    /* parent code */
    if (pid > 0) {
    
    /* close the unused end of the pipe */
    close(fd[READ_END]);
    
    /* make a buffer to store input file information */
    //char buffer[BUFFER_SIZE];
    
    /* open input file */
    FILE *in;
    FILE *out;
    in = fopen(infile, "r");
    out = fopen(outfile, "w");
    
    /* make sure it's not null */
    if (in == NULL) {
    fprintf(stderr, "Error opening file %s\n", infile);
    return 1;
    }
    
    /* read from the file into the pipe thru the buffer */
    while (!feof(in)) {
    char buffer[BUFFER_SIZE];
    fgets(buffer, BUFFER_SIZE, in);
    printf("%s\n",buffer);
    //printf("%d\n",write(fd[WRITE_END], buffer, strlen(buffer)+1));
    int val = fprintf(out,"%s",buffer);
    printf("===%d\n",val);
    fflush(in);
    }
    
    /* close the input file */
    fclose(in);
    
    /* close the pipe */
    close(fd[WRITE_END]);
    }
    
    /* child process has pid == 0 */
    else {
    
    /* create a buffer to read from the pipe and store into the out file */
    //char buffer[BUFFER_SIZE];
    
    /* close the unused end of the pipe */
    close(fd[WRITE_END]);
    
    /* initialize the output file */
    FILE *out;
    
    /* w+ means open a file for writing and create it if it doesn't exist */
    out = fopen(outfile, "w+");
    
    /* read from the pipe to the buffer */
    //read(fd[READ_END], buffer, BUFFER_SIZE);
    
    /* write from the buffer to the file */
    //fprintf(out, "%s", buffer);
    
    while(1) {
    char buffer[BUFFER_SIZE];
    if (read(fd[READ_END], buffer, BUFFER_SIZE) != 0)
    fprintf(out,"%s",buffer);
    else
    break;
    }
    
    
    /* close the file and the pipe */
    fclose(out);
    close(fd[READ_END]);
    }
    }
    }
    Thank you.
    Last edited by ungalnanban; 02-18-2010 at 01:46 AM. Reason: sysntx error and I found one more problem

  3. #3
    Registered User
    Join Date
    Feb 2010
    Posts
    15
    Dear friend,

    You have create the fork, it is correct. But in the parent you are tried to read the file and in the child you are tried to write. That also correct.

    But in the parent process you close the write fd wrongly. Here no need to close the fd. Then another mistake is you are check the condition in the while loop using the feof function. So that time it will execute the loop another one time also. Instead of this you can use the fgets in the main loop.

    Because if the the file pointer get the EOF it will exit from the loop. So it is the correct way to execute the loop. I have attach my coding here. It is working fine.

    Code:
    #include <sys/types.h>
    #include <stdio.h>
    #include <string.h>
    #include <unistd.h>
    
    #define BUFFER_SIZE 80
    #define READ_END 0
    #define WRITE_END 1
    
    int main(int argc, char *argv[]) {
    
    /* argc must be 3 to ensure the correct usage */
    if (argc != 3) {
    printf("The usage of this program is:\n");
    printf("FileCopy input.txt copy.txt\n");
    return 1;
    }
    
    else {
    /* initialize the pipe and fork variables */
    int fd[2];/* argv[0] is the program name, argv[1] and argv[2] are the file names */
    char *infile = argv[1];
    char *outfile = argv[2];
    
    /* create a pipe */
    if (pipe(fd) == -1) {
    fprintf(stderr, "Pipe failed");
    return 1;
    }
    
    /* fork */
    pid = fork();
    
    /* if pid < 0 there is an error */
    if (pid < 0) {
    fprintf(stderr, "Fork error");
    return 1;
    }
    
    /* parent code */
    if (pid > 0) {
    /* close the unused end of the pipe */
    close(fd[READ_END]);
    /* make a buffer to store input file information */
    
    char buffer[BUFFER_SIZE];
    
    /* open input file */
    FILE *in;
    in = fopen(infile, "r");
    
    /* make sure it's not null */
    if (in == NULL) {
    fprintf(stderr, "Error opening file %s\n", infile);
    return 1;
    }
    
    /* read from the file into the pipe thru the buffer */
    while (fgets(buffer, BUFFER_SIZE, in)){
    write(fd[WRITE_END], buffer, strlen(buffer)+1);
    printf("buf1:%s\n",buffer);
    buffer[0]='\0';
    //fprintf(in, buffer, strlen(buffer)+1);
    }
    
    /* close the input file *///close(fd[WRITE_END]);
    }
    
    /* child process has pid == 0 */
    else {
    
    /* create a buffer to read from the pipe and store into the out file */
    //char buffer[BUFFER_SIZE];
    
    /* close the unused end of the pipe */
    close(fd[WRITE_END]);
    
    /* initialize the output file */
    FILE *out;
    
    /* w+ means open a file for writing and create it if it doesn't exist */
    out = fopen(outfile, "w+");
    
    /* read from the pipe to the buffer */
    //read(fd[READ_END], buffer, BUFFER_SIZE);
    
    /* write from the buffer to the file */
    //fprintf(out, "%s", buffer);
    while(1) {
    char buffer[BUFFER_SIZE];
    if (read(fd[READ_END], buffer, BUFFER_SIZE) != 0)
    {
    fprintf(out,"%s",buffer);
    fflush(out);
    }
    else
    break;
    }
    
    /* close the file and the pipe */
    fclose(out);
    close(fd[READ_END]);
    }
    }
    }
    
    
    
    fclose(in);
    
    /* close the pipe */
    
    pid_t pid;
    Thanks

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