DOC: Clarification of the /H Identifier Length Option (51724)

SUMMARY

In Microsoft C, the /H option is used to set the maximum length of identifiers. Using /H can only decrease the maximum allowable length of identifiers, not increase it. An identifier declared with the CDECL type has an underscore (_) appended to the front at compile time. This character is part of the identifier and takes a significant location. Therefore, the maximum length of an identifier declared with the standard C declaration syntax is 32 characters.

In C/C++ version 7.0, the default maximum length is also 32 characters. However, in this version, the /H option may be used to increase this to a maximum of 247 characters.

In Visual C++ 16-bit and Visual C++ 32-bit, there is no default maximum length--identifiers can be up to 2047 characters in length. Compiling a program with an identifier containing more than 2047 characters will generate fatal error C1064, compiler limit : token overflowed internal buffer.

/* When compiled with /H5, the following code will produce either
 *    error L2025: _func : symbol defined more than once
 *      -or-
 *   error LNK2005: _func already defined in '.obj file'
 *   fatal error LNK1169: one or more multiply defined symbols found
 *      -or-
 *   fatal error LNK1179: invalid or corrupt file: duplicate comdat

void func1(void);
void func2(void);

void main(void)
{
     func1();
}

void func1(void)
{
}

void func2(void)
{
}