reading files into memory

This is a discussion on reading files into memory within the C Programming forums, part of the General Programming Boards category; Basically, i have a file of an unkown size, with no header etc. to get information from about the size ...

  1. #1
    Matt Conway bobthebullet990's Avatar
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    reading files into memory

    Basically, i have a file of an unkown size, with no header etc. to get information from about the size of the file! ...All i need to do is to allocate memory using malloc, creating a pointer to the allocated memory and then read the file char by char into the memory!

    Does anyone know the best way to find the length of the file????

    I have tried a few different ways, but they don't seem to work! This is what i am doing at the moment, but when i print the memory, it is just blank, no data gets put into it!!!!

    Code:
    FILE *fp;
    char    *buffer;
    long    numbytes;
    
    /* open an existing file for reading NOTE: filename is not the file i am opening, its just for example!*/
    fp = fopen("filename", "r");
     
    /* quit if the file does not exist */
    if(fp == NULL)
        return 1;
     
    /* Get the number of bytes */
    fseek(fp, 0L, SEEK_END);
    numbytes = ftell(fp);
     
    /* reset the file position indicator to 
    the beginning of the file */
    fseek(fp, 0L, SEEK_SET);	
     
    /* grab sufficient memory for the 
    buffer to hold the text */
    buffer = (char*)calloc(numbytes, sizeof(char));	
     
    /* memory error */
    if(buffer == NULL)
        return 1;
     
    /* copy all the text into the buffer */
    fread(buffer, sizeof(char), numbytes, fp);
    fclose(fp);
    
    /* confirm we have read the file by
    outputing it to the console */
    printf("contents of file:\n%s", buffer);
     
    /* free the memory we used for the buffer */
    free(buffer);

  2. #2
    Software Developer jverkoey's Avatar
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    fp = fopen("filename", "r");

    Use "rb" instead of "r".

  3. #3
    ZuK
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    If you want to output the files contents as a string using
    Code:
    printf("contents of file:\n%s", buffer);
    you will have to append a terminating '\0'.
    Kurt

  4. #4
    Frequently Quite Prolix dwks's Avatar
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    Use "rb" instead of "r".
    With an extra 'b' the file opens in binary mode (which is required for fread).

    And you shouldn't cast malloc(), calloc(), or realloc().
    dwk

    Seek and ye shall find. quaere et invenies.

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