什么是C ++成语替换snprintf（3）？ [英] What is the C++ idiom to replace snprintf(3)?

问题描述

我有一些C ++代码，当解析某个文件头失败时需要生成错误消息。在这种情况下，我需要确保头中的某个4字节字段是OggS，如果不是，则返回错误消息，如invalid capture_pattern：'FooB'; expecting'OggS'。我的代码看起来像这样：

  const string OggPage :: parseHeader（void）{
 read（fd，capture_pattern ，sizeof（capture_pattern））; //错误处理省略
 if（strncmp（capture_pattern，CAPTURE_PATTERN，sizeof（capture_pattern））！= 0）{
 char err [256] 
 snprintf（err，sizeof（err），无法从文件描述符％d读取％d个字节％s：\\ n，sizeof（capture_pattern），fd，err）; 
 return err; 
} 
 
 return一切都很好！ 
} 
  

从其他数据类型构建字符串的标准C ++语言是什么？我不像这里的 printf（3） - 样式格式，所以随意建议任何工作。

c> cstream> c> cstream> c> cstream> c>如果进一步的流不会用于读取值（例如 istream 部分不会被使用） ostringstream 更合适。

  #include< sstream> 
 #include< string> 
 #include< iostream> 
 
 int main（）{
 std :: stringstream str_stream; 
 int number = 5; 
 
 str_stream<< String with number<<数字<< std :: endl ;; 
 
 std :: string str = str_stream.str（）; 
 std :: cout<< str; 
} 
  

I have some C++ code which needs to generate an error message when parsing a certain file header fails. In this case, I need to ensure that a certain 4 byte field in the header is "OggS", and if it is not, return an error message like "invalid capture_pattern: 'FooB'; expecting 'OggS'". My code looks something like this:

const string OggPage::parseHeader(void) {
  read(fd, capture_pattern, sizeof(capture_pattern)); // error handling omitted
  if (strncmp(capture_pattern, CAPTURE_PATTERN, sizeof(capture_pattern)) != 0) {
    char err[256];
    snprintf(err, sizeof(err), "Failed to read %d bytes from file descriptor %d: %s\n", sizeof(capture_pattern), fd, err);
    return err;
  }

  return "Everything was A-OK!";
}

What is the standard C++ idiom for building a string from other datatypes? I'm not wedded to the printf(3)-style format here, so feel free to suggest anything that works.

解决方案

You can use stringstream or ostringstreamfrom C++ Standard library. If further stream will not be used to read values from it (e.g. it's istream part won't be used) ostringstream is more suitable.

#include <sstream>
#include <string>
#include <iostream>

int main() {
 std::stringstream str_stream;
 int number = 5;

 str_stream << " String with number " << number << std::endl;;

 std::string str = str_stream.str();
 std::cout << str; 
}

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