C++ 如何有效地将大std:：string的一部分转换为float？
这是我用来将缓冲区字符串中的文本转换为float并将其放入向量中的代码。字符串的重要部分本身具有以下结构：C++ 如何有效地将大std:：string的一部分转换为float？,c++,parsing,wavefront,C++,Parsing,Wavefront,这是我用来将缓冲区字符串中的文本转换为float并将其放入向量中的代码。字符串的重要部分本身具有以下结构： void OBJLoader::load_vec(const char* line_prefix) { size_t jump = 0; size_t strpos = 0; if (line_prefix == "v ") { while ((strpos = buffer.find(line_prefix, strpos)) != string::npos) {
void OBJLoader::load_vec(const char* line_prefix) {
size_t jump = 0;
size_t strpos = 0;
if (line_prefix == "v ") {
while ((strpos = buffer.find(line_prefix, strpos)) != string::npos) {
strpos++;
vcoord_vec.emplace_back(stof(&buffer.at(strpos), &jump));
strpos += jump;
vcoord_vec.emplace_back(stof(&buffer.at(strpos), &jump));
strpos += jump;
vcoord_vec.emplace_back(stof(&buffer.at(strpos), &jump));
strpos += jump;
}
return;
}
//(...)
v -0.893339 0.784809 0.891470
v -0.893339 -0.784809 0.891470
v -0.692655 -0.634043 0.017402
v 0.692655 0.586786 -0.017402
v -0.710057 0.651445 0.000000
v 0.710057 -0.604188 0.000000
v 0.017402 -0.571364 -0.674429
v -0.017402 0.618621 0.674429
v 0.000000 -0.636023 0.691831
在489ms内加载其中的4718598个。什么是C++方法将字符串中已知的一部分转换成任何类型的数字，具有类似的效率？< P>对于像你所使用的具有空间分隔值的真正基本格式，可以使用C++流： 包括 /*...*/ 字符id； 浮动v[3]； 标准：：istringstream issv 123.4 12.5 0262.2； iss>>id； 如果id=='v'{ iss>>v[0]>>v[1]>>v[2]； } 您使用std:：stof时出错。当它需要一个常量std:：string&时，您正在向它传递一个char* 其结果是在每次调用std:：stof时，从char*隐式转换为std:：string，将从strpos开始的缓冲区的全部内容复制到其空终止符，并将其复制到通过转换函数参数创建的临时值中
如果C++17可用，则更喜欢std:：from_chars，否则我建议使用std:：strof进行转换，这并不意味着您必须继续使用strstr。std:：stof被指定为无论如何都要调用std:：strtof。这里有一个我在3D图形引擎中使用的实用程序类。对于我的示例，您需要有一个可用的GLM库版本，否则您可以注释掉所有与GLM相关的内容，以完成单个值的简单基本转换。但是，我在这里演示如何将字符串转换为不同的数字类型，包括用户定义的类型 无法构造此实用程序类对象的实例，因为它的构造函数已删除，并且没有成员变量。它只是一个类似或相关函数的集合，主要是字符串操作方法 如果您花时间通读这个类，您将看到我正在使用静态函数将字符串转换为所需的类型
该类确实有2个私有函数模板，string_to_value（在类外部的头中定义）和get_value（在cpp文件中定义），因为有3个基于返回类型的重载函数或模板专门化函数。它们分别是int、unsigned和float。我还包括了重载运算符。如果有可用的话，您应该使用std:：from_chars。200ms将单个值加载到向量中：stof可能很慢，但这似乎太过分了。你确定这不是打字错误吗？您是否在第_prefix==“v”行上进行了优化编译“这可能适用于某些编译器，但您应该避免。标准并没有规定相等的字符串文字必须具有相等的地址。@我是肯定的，正在进行优化，感觉每次调用都要复制250MB的字符串。实际上visual studio中的内存监视器在使用中显示出奇怪的峰值。@BigTemp What type是缓冲区？您是否尝试过将.at…替换为带[…]的绑定检查标准容器/字符串，而[…]没有？
void OBJLoader::load_vec(const char* line_prefix) {
char* cbuffer = const_cast<char*>(buffer.c_str());
if (line_prefix == "v ") {
while (cbuffer = strstr(cbuffer, line_prefix)) {
cbuffer++;
vcoord_vec.emplace_back(strtof(cbuffer, &cbuffer));
vcoord_vec.emplace_back(strtof(cbuffer, &cbuffer));
vcoord_vec.emplace_back(strtof(cbuffer, &cbuffer));
}
return;
}
//(...)
#include <iostream>
#include "Utility.h"
int main() {
using namespace util;
try {
std::string str1("3,4,5");
std::string str2("-4,-2,7");
std::string str3("2.4,7.8,9.2");
glm::uvec3 uvec3 = Utility::convert_to_uvec3(str1);
glm::ivec3 ivec3 = Utility::convert_to_ivec3(str2);
glm::vec3 vec3 = Utility::convert_to_vec3(str3);
std::cout << uvec3 << '\n';
std::cout << ivec3 << '\n';
std::cout << vec3 << '\n';
// test an exception case:
glm::vec4 v4 = Utility::convert_to_vec4(str2);
} catch (const std::exception& e) {
std::cerr << e.what() << std::endl;
return EXIT_FAILURE;
}
return EXIT_SUCCESS;
}
(3,4,5)
(-4,-2,7)
(2.4,7.8,9.2)
util::Utility::convert_to_vec4 Bad conversion of [-4,-2,7] to vec4
#ifndef UTILITY_H
#define UTILITY_H
#include <string>
#include <algorithm>
#include <glm/glm.hpp>
namespace util {
class Utility {
public:
static std::string to_upper(const std::string& str);
static std::string to_lower(const std::string& str);
static std::string trim(const std::string& str, const std::string elements_to_trim = " \t\n\r");
static unsigned convert_to_unsigned(const std::string& str);
static int convert_to_int(const std::string& str);
static float convert_to_float(const std::string& str);
static glm::vec2 convert_to_vec2(const std::string& str);
static glm::vec3 convert_to_vec3(const std::string& str);
static glm::vec4 convert_to_vec4(const std::string& str);
static glm::ivec2 convert_to_ivec2(const std::string& str);
static glm::ivec3 convert_to_ivec3(const std::string& str);
static glm::ivec4 convert_to_ivec4(const std::string& str);
static glm::uvec2 convert_to_uvec2(const std::string& str);
static glm::uvec3 convert_to_uvec3(const std::string& str);
static glm::uvec4 convert_to_uvec4(const std::string& str);
private:
Utility() = delete;
Utility(const Utility& c) = delete;
Utility& operator=(const Utility& c) = delete;
template<typename T>
static bool string_to_value(const std::string& str, T* value, unsigned num_values);
template<typename T>
static T get_value(const std::string& str, std::size_t& remainder);
};
template<typename T>
static bool Utility::string_to_value(const std::string& str, T* value, unsigned num_values) {
int num_commas = std::count(str.begin(), str.end(), ',');
if (num_commas != num_values - 1) return false;
std::size_t remainder;
value[0] = get_value<T>(str, remainder);
if (num_values == 1) {
if (str.size() != remainder) {
return false;
}
} else {
std::size_t offset = remainder;
if (str.at(offset) != ',') {
return false;
}
unsigned last_indx = num_values - 1;
for (unsigned u = 1; u < num_values; ++u) {
value[u] = get_value<T>(str.substr(++offset), remainder);
offset += remainder;
if ((u < last_indx && str.at(offset) != ',') ||
(u == last_indx && offset != str.size())) {
return false;
}
}
}
return true;
}
} // namespace util
std::ostream& operator<<(std::ostream& out, const glm::ivec2& v2Value);
std::ostream& operator<<(std::ostream& out, const glm::ivec3& v3Value);
std::ostream& operator<<(std::ostream& out, const glm::ivec4& v4Value);
std::ostream& operator<<(std::ostream& out, const glm::vec2& v2Value);
std::ostream& operator<<(std::ostream& out, const glm::vec3& v3Value);
std::ostream& operator<<(std::ostream& out, const glm::vec4& v4Value);
std::ostream& operator<<(std::ostream& out, const glm::uvec2& v2Value);
std::ostream& operator<<(std::ostream& out, const glm::uvec3& v3Value);
std::ostream& operator<<(std::ostream& out, const glm::uvec4& v4Value);
#endif // UTILITY_H
#include "Utility.h"
#include <exception>
#include <sstream>
namespace util {
std::string Utility::to_upper(const std::string& str) {
std::string result = str;
std::transform(str.begin(), str.end(), result.begin(), ::toupper);
return result;
}
std::string Utility::to_lower(const std::string& str) {
std::string result = str;
std::transform(str.begin(), str.end(), result.begin(), ::tolower);
return result;
}
std::string Utility::trim(const std::string& str, const std::string elements_to_trim) {
std::basic_string<char>::size_type first_index = str.find_first_not_of(elements_to_trim);
if (first_index == std::string::npos) {
return std::string(); // nothing left
}
std::basic_string<char>::size_type last_index = str.find_last_not_of(elements_to_trim);
return str.substr(first_index, last_index - first_index + 1);
}
template<>
float Utility::get_value(const std::string& str, std::size_t& remainder) {
return std::stof(str, &remainder);
} // getValue<float>
template<>
int Utility::get_value(const std::string& str, std::size_t& remainder) {
return std::stoi(str, &remainder);
} // getValue<int>
template<>
unsigned Utility::get_value(const std::string& str, std::size_t& remainder) {
return std::stoul(str, &remainder);
} // getValue<unsigned>
unsigned Utility::convert_to_unsigned(const std::string& str) {
unsigned u = 0;
if (!string_to_value(str, &u, 1)) {
std::ostringstream stream;
// __FUNCTION__ works on windows otherwise user can exchange - modify to use __PRETTY_FUNCTION__
stream << __FUNCTION__ << " Bad conversion of [" << str << "] to unsigned";
throw std::exception(stream.str().c_str());
}
return u;
}
int Utility::convert_to_int(const std::string& str) {
int i = 0;
if (!string_to_value(str, &i, 1)) {
std::ostringstream stream;
// __FUNCTION__ works on windows otherwise user can exchange - modify to use __PRETTY_FUNCTION__
stream << __FUNCTION__ << " Bad conversion of [" << str << "] to int";
throw std::exception(stream.str().c_str());
}
return i;
}
float Utility::convert_to_float(const std::string& str) {
float f = 0;
if (!string_to_value(str, &f, 1)) {
std::ostringstream stream;
// __FUNCTION__ works on windows otherwise user can exchange - modify to use __PRETTY_FUNCTION__
stream << __FUNCTION__ << " Bad conversion of [" << str << "] to float";
throw std::exception(stream.str().c_str());
}
return f;
}
glm::vec2 Utility::convert_to_vec2(const std::string& str) {
glm::vec2 v2;
if (!string_to_value(str, &v2[0], 2)) {
std::ostringstream stream;
// __FUNCTION__ works on windows otherwise user can exchange - modify to use __PRETTY_FUNCTION__
stream << __FUNCTION__ << " Bad conversion of [" << str << "] to vec2";
throw std::exception(stream.str().c_str());
}
return v2;
}
glm::vec3 Utility::convert_to_vec3(const std::string& str) {
glm::vec3 v3;
if (!string_to_value(str, &v3[0], 3)) {
std::ostringstream stream;
// __FUNCTION__ works on windows otherwise user can exchange - modify to use __PRETTY_FUNCTION__
stream << __FUNCTION__ << " Bad conversion of [" << str << "] to vec3";
throw std::exception(stream.str().c_str());
}
return v3;
}
glm::vec4 Utility::convert_to_vec4(const std::string& str) {
glm::vec4 v4;
if (!string_to_value(str, &v4[0], 4)) {
std::ostringstream stream;
// __FUNCTION__ works on windows otherwise user can exchange - modify to use __PRETTY_FUNCTION__
stream << __FUNCTION__ << " Bad conversion of [" << str << "] to vec4";
throw std::exception(stream.str().c_str());
}
return v4;
}
glm::ivec2 Utility::convert_to_ivec2(const std::string& str) {
glm::ivec2 v2;
if (!string_to_value(str, &v2[0], 2)) {
std::ostringstream stream;
// __FUNCTION__ works on windows otherwise user can exchange - modify to use __PRETTY_FUNCTION__
stream << __FUNCTION__ << " Bad conversion of [" << str << "] to ivec2";
throw std::exception(stream.str().c_str());
}
return v2;
}
glm::ivec3 Utility::convert_to_ivec3(const std::string& str) {
glm::ivec3 v3;
if (!string_to_value(str, &v3[0], 3)) {
std::ostringstream stream;
// __FUNCTION__ works on windows otherwise user can exchange - modify to use __PRETTY_FUNCTION__
stream << __FUNCTION__ << " Bad conversion of [" << str << "] to ivec3";
throw std::exception(stream.str().c_str());
}
return v3;
}
glm::ivec4 Utility::convert_to_ivec4(const std::string& str) {
glm::ivec4 v4;
if (!string_to_value(str, &v4[0], 4)) {
std::ostringstream stream;
// __FUNCTION__ works on windows otherwise user can exchange - modify to use __PRETTY_FUNCTION__
stream << __FUNCTION__ << " Bad conversion of [" << str << "] to ivec4";
throw std::exception(stream.str().c_str());
}
return v4;
}
glm::uvec2 Utility::convert_to_uvec2(const std::string& str) {
glm::uvec2 v2;
if (!string_to_value(str, &v2[0], 2)) {
std::ostringstream stream;
// __FUNCTION__ works on windows otherwise user can exchange - modify to use __PRETTY_FUNCTION__
stream << __FUNCTION__ << " Bad conversion of [" << str << "] to uvec2";
throw std::exception(stream.str().c_str());
}
return v2;
}
glm::uvec3 Utility::convert_to_uvec3(const std::string& str) {
glm::uvec3 v3;
if (!string_to_value(str, &v3[0], 3)) {
std::ostringstream stream;
// __FUNCTION__ works on windows otherwise user can exchange - modify to use __PRETTY_FUNCTION__
stream << __FUNCTION__ << " Bad conversion of [" << str << "] to uvec3";
throw std::exception(stream.str().c_str());
}
return v3;
}
glm::uvec4 Utility::convert_to_uvec4(const std::string& str) {
glm::uvec4 v4;
if (!string_to_value(str, &v4[0], 4)) {
std::ostringstream stream;
// __FUNCTION__ works on windows otherwise user can exchange - modify to use __PRETTY_FUNCTION__
stream << __FUNCTION__ << " Bad conversion of [" << str << "] to uvec4";
throw std::exception(stream.str().c_str());
}
return v4;
}
} // namespace util
std::ostream& operator<<(std::ostream& out, const glm::ivec2& v2Value) {
out << "("
<< v2Value.x << ","
<< v2Value.y << ")";
return out;
}
std::ostream& operator<<(std::ostream& out, const glm::ivec3& v3Value) {
out << "("
<< v3Value.x << ","
<< v3Value.y << ","
<< v3Value.z << ")";
return out;
}
std::ostream& operator<<(std::ostream& out, const glm::ivec4& v4Value) {
out << "("
<< v4Value.x << ","
<< v4Value.y << ","
<< v4Value.z << ","
<< v4Value.w << ")";
return out;
}
std::ostream& operator<<(std::ostream& out, const glm::vec2& v2Value) {
out << "("
<< v2Value.x << ","
<< v2Value.y << ")";
return out;
}
std::ostream& operator<<(std::ostream& out, const glm::vec3& v3Value) {
out << "("
<< v3Value.x << ","
<< v3Value.y << ","
<< v3Value.z << ")";
return out;
}
std::ostream& operator<<(std::ostream& out, const glm::vec4& v4Value) {
out << "("
<< v4Value.x << ","
<< v4Value.y << ","
<< v4Value.z << ","
<< v4Value.w << ")";
return out;
}
std::ostream& operator<<(std::ostream& out, const glm::uvec2& v2Value) {
out << "("
<< v2Value.x << ","
<< v2Value.y << ")";
return out;
}
std::ostream& operator<<(std::ostream& out, const glm::uvec3& v3Value) {
out << "("
<< v3Value.x << ","
<< v3Value.y << ","
<< v3Value.z << ")";
return out;
}
std::ostream& operator<<(std::ostream& out, const glm::uvec4& v4Value) {
out << "("
<< v4Value.x << ","
<< v4Value.y << ","
<< v4Value.z << ","
<< v4Value.w << ")";
return out;
}