IDebugExpressionContext2::ParseText
Parses an expression in text form for later evaluation.
Syntax
int ParseText(
string pszCode,
enum_PARSEFLAGS dwFlags,
uint nRadix,
out IDebugExpression2 ppExpr,
out string pbstrError,
out uint pichError
);
Parameters
pszCode
[in] The expression to be parsed.
dwFlags
[in] A combination of flags from the PARSEFLAGS enumeration that controls parsing.
nRadix
[in] The radix to be used in parsing any numerical information in pszCode.
ppExpr
[out] Returns the IDebugExpression2 object that represents the parsed expression, which is ready for binding and evaluation.
pbstrError
[out] Returns the error message if the expression contains an error.
pichError
[out] Returns the character index of the error in pszCode if the expression contains an error.
Return Value
If successful, returns S_OK; otherwise, returns an error code.
Remarks
When this method is called, a debug engine (DE) should parse the expression and validate it for correctness. The pbstrError and pichError parameters may be filled in if the expression is invalid.
Note that the expression is not evaluated, only parsed. A later call to the EvaluateSync or EvaluateAsync methods evaluates the parsed expression.
Example
The following example shows how to implement this method for a simple CEnvBlock object that exposes the IDebugExpressionContext2 interface. This example considers the expression to be parsed as the name of an environment variable and retrieves the value from that variable.
HRESULT CEnvBlock::ParseText(
LPCOLESTR pszCode,
PARSEFLAGS dwFlags,
UINT nRadix,
IDebugExpression2 **ppExpr,
BSTR *pbstrError,
UINT *pichError)
{
HRESULT hr = E_OUTOFMEMORY;
// Create an integer variable with a value equal to one plus
// twice the length of the passed expression to be parsed.
int iAnsiLen = 2 * (wcslen(pszCode)) + 1;
// Allocate a character string of the same length.
char *pszAnsiCode = (char *) malloc(iAnsiLen);
// Check for successful memory allocation.
if (pszAnsiCode) {
// Map the wide-character pszCode string to the new pszAnsiCode character string.
WideCharToMultiByte(CP_ACP, 0, pszCode, -1, pszAnsiCode, iAnsiLen, NULL, NULL);
// Check to see if the app can successfully get the environment variable.
if (GetEnv(pszAnsiCode)) {
// Create and initialize a CExpression object.
CComObject<CExpression> *pExpr;
CComObject<CExpression>::CreateInstance(&pExpr);
pExpr->Init(pszAnsiCode, this, NULL);
// Assign the pointer to the new object to the passed argument
// and AddRef the object.
*ppExpr = pExpr;
(*ppExpr)->AddRef();
hr = S_OK;
// If the program cannot successfully get the environment variable.
} else {
// Set the errror message and return E_FAIL.
*pbstrError = SysAllocString(L"No such environment variable.");
hr = E_FAIL;
}
// Free the local character string.
free(pszAnsiCode);
}
return hr;
}