C - Reading entire file come with garbage at the end

Question

So im trying to read an entire text file using this function:

FILE *fp = fopen(path, "r");
fseek(fp, 0, SEEK_END);
int tamanioArchivo = sizeof(char) * ftell(fp);
fseek(fp, 0, SEEK_SET);
char* archivo = malloc(tamanioArchivo + 1);
fread(archivo, tamanioArchivo + 1, 1, fp);
//do something with archivo
fclose(fp);
free(archivo);

I debugged it and the problem seems to be on the fread line. It brings back the file and adds some garbage at the end. Any ideas what im doing wrong?

Answer 1

Generally C doesn't care what the contents of a file are. Whether it's text or binary data, it's read the same way. Meaning if you want to read a string and get something nicely null-terminated, you need to handle that yourself.

fread(archivo, tamanioArchivo+1, 1, fp);

This reads one extra byte (again, null-termination is a C thing, the file system does not enforce this). Get rid of the plus 1. Then you must ensure that it's null-terminated:

archivo[tamanioArchivo] = '\0';

Answer 2

The "garbage" comes from improperly examining/printing archivo and code not noting how much was read.

fread() saves into archivo data, but that data is not certainly null character terminated - a C string. Append a '\0' if archivo is to point to a string.

But where? After the last character read - which is determined by the return value of fread(), not after the number of characters requested.

Even without an error, the return value may be less than the number of requested characters due to text mode end-of-line translation of "\r\n" into "\n". The value returned from ftell() is not necessarily the numbers of characters that will be read in text mode.

No need to attempt to read tamanioArchivo+1 characters. Use tamanioArchivo.

Also see @ Andrew Henle good comment about fread(ptr, element_size, number_of_elements, stream) parameter order.

// Note that the file is opened in text mode, not binary mode
FILE *fp = fopen (path, "r");

fseek(fp, 0, SEEK_END);
// int tamanioArchivo = sizeof(char) * ftell(fp);
long tamanioArchivo = ftell(fp);
fseek(fp, 0, SEEK_SET); // or `rewind(fp);

// Good to allocate +1 for the null chracter
char* archivo = malloc(tamanioArchivo + 1u);

// Save the return value and drop the +1
// fread(archivo, tamanioArchivo+1, 1, fp);
size_t read_count = fread(archivo, 1, tamanioArchivo, fp);

// bad
// bytes read may be less than the offset due to CR/LF-->LF or input error
archivo[tamanioArchivo] = '\0';

// good
archivo[read_count] = '\0';

//do something with archivo
puts(archivo); 

fclose (fp);
free(archivo);

---

Robust code would check the return value of fopen(), malloc(), fseek(), ftell() for unusual return values. The seek to the end, ftell() method for determining file length has additional limitations. Alternatives depend on various unposted coding goals.

Answer 3

Try this example:

/* Open Fpga config file */
fpconf = fopen(file, "rb");
if (fpconf == NULL) {
     return ERROR;
}

/* set SEEK_END to read the file size using ftell */
fseek(fpconf, 0L, SEEK_END);

bsize = ftell(fpconf);
print_dbg("Size of file: %d bytes\n", (int)bsize);

/* set file offset 0 */
fseek(fpconf, 0L, SEEK_SET);

data = (uint8_t *) malloc(sizeof(uint8_t) * bsize);
if (data == NULL) {
    print_err("Error in malloc\n");
    return ERROR;
}

/* Read data from file and store into buffer */
fread(data, bsize, 1, fpconf);

/* Close file */
fclose(fpconf);