以下代码将字符串形式的尺寸描述转换成字节数

#include <stdio.h>

#define SECTOR_SIZE_DEFAULT   512LL
#define KILOBYTE_SIZE 1000LL
#define MEGABYTE_SIZE 1000000LL
#define GIGABYTE_SIZE 1000000000LL
#define TERABYTE_SIZE 1000000000000LL
#define KIBIBYTE_SIZE 1024LL
#define MEBIBYTE_SIZE 1048576LL
#define GIBIBYTE_SIZE 1073741824LL
#define TEBIBYTE_SIZE 1099511627776LL

typedef enum {
    DIGIT_UNIT_BYTE,
    DIGIT_UNIT_KILOBYTE,
    DIGIT_UNIT_MEGABYTE,
    DIGIT_UNIT_GIGABYTE,
    DIGIT_UNIT_TERABYTE,
    DIGIT_UNIT_KIBIBYTE,
    DIGIT_UNIT_MEBIBYTE,
    DIGIT_UNIT_GIBIBYTE,
    DIGIT_UNIT_TEBIBYTE
} DigitUnit;

/* Inefficiently removes all spaces from a string, in-place. */
static void
strip_string (char* str)
{
    int i;

    for (i = 0; str[i] != 0; i++) {
        if (isspace (str[i])) {
            int j;
            for (j = i + 1; str[j] != 0; j++)
                str[j - 1] = str[j];
        }
    }
}

/* Find non-number suffix.  Eg: find_suffix("32Mb") returns a pointer to
 * "Mb". */
static char*
find_suffix (const char* str)
{
    while (str[0] != 0 && (isdigit (str[0]) || strchr(",.-", str[0])))
        str++;
    return (char *) str;
}

static DigitUnit
parse_unit_suffix (const char* suffix)
{
    if (strlen (suffix) > 1 && tolower (suffix[1]) == ‘i‘) {
        switch (tolower (suffix[0])) {
            case ‘k‘: return DIGIT_UNIT_KIBIBYTE;
            case ‘m‘: return DIGIT_UNIT_MEBIBYTE;
            case ‘g‘: return DIGIT_UNIT_GIBIBYTE;
            case ‘t‘: return DIGIT_UNIT_TEBIBYTE;
        }
    } else if (strlen (suffix) > 0) {
        switch (tolower (suffix[0])) {
            case ‘b‘: return DIGIT_UNIT_BYTE;
            case ‘k‘: return DIGIT_UNIT_KILOBYTE;
            case ‘m‘: return DIGIT_UNIT_MEGABYTE;
            case ‘g‘: return DIGIT_UNIT_GIGABYTE;
            case ‘t‘: return DIGIT_UNIT_TERABYTE;
        }
    }

    return -1;
}

long long unit_parse (const char *str)
{
    char *suffix;
    long long byte = -1;
    long long byte_block = 1;

    strip_string (str);
    suffix = find_suffix (str);

    DigitUnit unit = parse_unit_suffix (suffix);

    switch (unit) {
    case DIGIT_UNIT_BYTE:
        break;
    case DIGIT_UNIT_KILOBYTE:
        byte_block = KILOBYTE_SIZE;
        break;
    case DIGIT_UNIT_MEGABYTE:
        byte_block = MEGABYTE_SIZE;
        break;
    case DIGIT_UNIT_GIGABYTE:
        byte_block = GIGABYTE_SIZE;
        break;
    case DIGIT_UNIT_TERABYTE:
        byte_block = TERABYTE_SIZE;
        break;
    case DIGIT_UNIT_KIBIBYTE:
        byte_block = KIBIBYTE_SIZE;
        break;
    case DIGIT_UNIT_MEBIBYTE:
        byte_block = MEBIBYTE_SIZE;
        break;
    case DIGIT_UNIT_GIBIBYTE:
        byte_block = GIBIBYTE_SIZE;
        break;
    case DIGIT_UNIT_TEBIBYTE:
        byte_block = TEBIBYTE_SIZE;
        break;
    }

    double temp = 0;
    if (sscanf (str, "%lf", &temp) == 1)
        byte = temp * byte_block;

    return byte;
}


int main(int argc, char **argv)
{
    if (argc > 1)
        printf ("%lld\n", unit_parse (argv[1]));
}

以下代码将字符串形式的尺寸描述转换成字节数

原文：http://www.cnblogs.com/the-capricornus/p/4064697.html