C + + code line wrapping

1, string is too long, newline display, how to do?
2, using the backslash, as follows:
String str = "abcd\
1234 ";
Note: No characters are allowed after the backslash. The tabs at the beginning of the next line are not included in the entire string, but the whitespace at the beginning of the next line is contained in the entire string.
3, use double quotation marks, as follows:
String str = "ABCD"
"1234";
Note: Two strings are automatically spliced, and there can be any number of empty characters ("") and white space characters between two strings (white space characters, tab characters, line breaks). Note the following differences:
NULL: No value
Null character: "", not containing any characters
Whitespace characters: space characters, tabs, line breaks

C + + code line wrapping