c++ learning -- find_first_not_of ， find_first_of，string::npos

例子：

	std::unordered_map<GLenum, std::string> OpenGLShader::PreProcess(const std::string& source) {

		std::unordered_map<GLenum, std::string> shaderSources;
		const char* typeToken = "#type";
		size_t typeTockenLength = strlen(typeToken);
		size_t pos = source.find(typeToken, 0);//find找不到会返回npos
		while (pos != std::string::npos) {
			size_t eol = source.find_first_of("\r\n", pos);
			HZ_CORE_ASSERT(eol != std::string::npos, "Syntax error");
			size_t begin = pos + typeTockenLength + 1;
			std::string type = source.substr(begin, eol - begin);
			HZ_CORE_ASSERT(ShaderTypeFromString(type), "Invalid shader type specified");

			size_t nextLinePos = source.find_first_not_of("\r\n", eol);
			pos = source.find(typeToken, nextLinePos);
			shaderSources[ShaderTypeFromString(type)] = source.substr(nextLinePos,
				pos - (nextLinePos == std::string::npos ? source.size() - 1 : nextLinePos));

		}
		return shaderSources;

	}

找到pos位置之后第一个等于"\r\n"的字符位置： 

size_t eol = source.find_first_of("\r\n", pos);

找到pos位置之后第一个不等于"\r\n"的字符位置： 

size_t nextLinePos = source.find_first_not_of("\r\n", eol);

 

 string::npos

1)可以表示string的结束位置

2）表示find()查找失败