Why can't I assign a scalar value to a class using shorthand, but instead declare it first, then set
- by ~delan-azabani
I am writing a UTF-8 library for C++ as an exercise as this is my first real-world C++ code. So far, I've implemented concatenation, character indexing, parsing and encoding UTF-8 in a class called "ustring". It looks like it's working, but two (seemingly equivalent) ways of declaring a new ustring behave differently. The first way:
ustring a;
a = "test";
works, and the overloaded "=" operator parses the string into the class (which stores the Unicode strings as an dynamically allocated int pointer). However, the following does not work:
ustring a = "test";
because I get the following error:
test.cpp:4: error: conversion from ‘const char [5]’ to non-scalar type ‘ustring’ requested
Is there a way to workaround this error? It probably is a problem with my code, though. The following is what I've written so far for the library:
#include <cstdlib>
#include <cstring>
class ustring {
int * values;
long len;
public:
long length() {
return len;
}
ustring * operator=(ustring input) {
len = input.len;
values = (int *) malloc(sizeof(int) * len);
for (long i = 0; i < len; i++)
values[i] = input.values[i];
return this;
}
ustring * operator=(char input[]) {
len = sizeof(input);
values = (int *) malloc(0);
long s = 0; // s = number of parsed chars
int a, b, c, d, contNeed = 0, cont = 0;
for (long i = 0; i < sizeof(input); i++)
if (input[i] < 0x80) { // ASCII, direct copy (00-7f)
values = (int *) realloc(values, sizeof(int) * ++s);
values[s - 1] = input[i];
} else if (input[i] < 0xc0) { // this is a continuation (80-bf)
if (cont == contNeed) { // no need for continuation, use U+fffd
values = (int *) realloc(values, sizeof(int) * ++s);
values[s - 1] = 0xfffd;
}
cont = cont + 1;
values[s - 1] = values[s - 1] | ((input[i] & 0x3f) << ((contNeed - cont) * 6));
if (cont == contNeed) cont = contNeed = 0;
} else if (input[i] < 0xc2) { // invalid byte, use U+fffd (c0-c1)
values = (int *) realloc(values, sizeof(int) * ++s);
values[s - 1] = 0xfffd;
} else if (input[i] < 0xe0) { // start of 2-byte sequence (c2-df)
contNeed = 1;
values = (int *) realloc(values, sizeof(int) * ++s);
values[s - 1] = (input[i] & 0x1f) << 6;
} else if (input[i] < 0xf0) { // start of 3-byte sequence (e0-ef)
contNeed = 2;
values = (int *) realloc(values, sizeof(int) * ++s);
values[s - 1] = (input[i] & 0x0f) << 12;
} else if (input[i] < 0xf5) { // start of 4-byte sequence (f0-f4)
contNeed = 3;
values = (int *) realloc(values, sizeof(int) * ++s);
values[s - 1] = (input[i] & 0x07) << 18;
} else { // restricted or invalid (f5-ff)
values = (int *) realloc(values, sizeof(int) * ++s);
values[s - 1] = 0xfffd;
}
return this;
}
ustring operator+(ustring input) {
ustring result;
result.len = len + input.len;
result.values = (int *) malloc(sizeof(int) * result.len);
for (long i = 0; i < len; i++)
result.values[i] = values[i];
for (long i = 0; i < input.len; i++)
result.values[i + len] = input.values[i];
return result;
}
ustring operator[](long index) {
ustring result;
result.len = 1;
result.values = (int *) malloc(sizeof(int));
result.values[0] = values[index];
return result;
}
char * encode() {
char * r = (char *) malloc(0);
long s = 0;
for (long i = 0; i < len; i++) {
if (values[i] < 0x80)
r = (char *) realloc(r, s + 1),
r[s + 0] = char(values[i]),
s += 1;
else if (values[i] < 0x800)
r = (char *) realloc(r, s + 2),
r[s + 0] = char(values[i] >> 6 | 0x60),
r[s + 1] = char(values[i] & 0x3f | 0x80),
s += 2;
else if (values[i] < 0x10000)
r = (char *) realloc(r, s + 3),
r[s + 0] = char(values[i] >> 12 | 0xe0),
r[s + 1] = char(values[i] >> 6 & 0x3f | 0x80),
r[s + 2] = char(values[i] & 0x3f | 0x80),
s += 3;
else
r = (char *) realloc(r, s + 4),
r[s + 0] = char(values[i] >> 18 | 0xf0),
r[s + 1] = char(values[i] >> 12 & 0x3f | 0x80),
r[s + 2] = char(values[i] >> 6 & 0x3f | 0x80),
r[s + 3] = char(values[i] & 0x3f | 0x80),
s += 4;
}
return r;
}
};
