Reading a text file line by line and saving to an array (C Language)

Question

Here's my issue: I'm currently working on a project for university. We're suppose to do a program that receives .pbm and .pgm files as input, and then we're suppose to handle them in some ways. But for now the main thing is to successfully receive them. Each .pbm and .pgm file's first line is a "magic number". A set of characters like P1, P2 (...) P6. Our goal is to receive a .pbm file as input, save the first line, dynamically allocate a string so it is just as big as its content (P6\n, for example), so we can then detect the magic number. The same applies to every other line. We basically just want a way to save each line into an array, making them just as big as their content. Me and my project partner are both beginners: file handling, pointers, dynamic memory and headers are still pretty hard to us. Thank you in advance.

---EDIT--- (Forgot the code, as an user pointed out)

int main(int argc, char const *argv[])
{
    readFile(argv[1], "EI_2012-13_ascii.pbm");
    return 0;
}

void readFile (const char* input_file, char* filename){
    char *line_buffer, *line;
    FILE *file_stream = NULL;

    if(!check_extension(filename, ".pbm") &&
     !check_extension(filename, ".pgm") && !check_extension(filename, ".ppm"))
        ERROR(ERR_EXT, "Invalid file extension!\n");


    file_stream = fopen(input_file, "r");
    if (file_stream == NULL)
        ERROR(ERR_EXT, "Couldn't open the file for reading");

    line_buffer = malloc(sizeof(2));
    fscanf(file_stream, "%s", line_buffer);
    //line = strchr(line_buffer, '\n');

    printf("%s\n", line_buffer);
    printf("%d\n", sizeof(line_buffer));

    fclose(file_stream);
}

With this code we were attempting to output a string and its size underneath it. Strangely we keep getting the same output: 4. We needed that the malloc received a proper argument, the size of the line until the '\n'.

Above is your problem description, you didn't mention where you stuck in implementing it. — Sunil Bojanapally, Nov 01 '13 at 18:13

score 2 · Accepted Answer · answered Nov 01 '13 at 19:13

2

You can detect the magic number reading the file line by line using Linux function getline() as shown below,

void readFile (const char* input_file, char* filename){
    char *line;
    FILE *file_stream = NULL;
    ssize_t read; size_t len = 0;

    file_stream = fopen(input_file, "r");
    if (file_stream == NULL)
         ERROR(ERR_EXT, "Couldn't open the file for reading");

     while((read = getline(&line, &len, file_stream)) != 1){
        printf("%s", line);
        printf("length of line: %zu\n", read);
     }
     if (line)
        free(line);  
     fclose(file_stream);
}

answered Nov 01 '13 at 19:13

Sunil Bojanapally

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Thank you! This solution is great since I'm working in linux enviroment. – Deegriz Nov 01 '13 at 21:05
a type i guess. the check condition in while should be against -1. – Madhur Rawat Feb 06 '16 at 18:41

Reading a text file line by line and saving to an array (C Language)

1 Answers1