下面有2个程序。在第一个我已经条纹化了除问题循环之外的所有东西，当我这样做时它起作用。在第二个程序中（仍然是我正在处理的程序）我使用相同的逻辑，但是名为for_loop_buffer的子字符串永远不会加载。
基本上我正在解析一个包含cdf文件记录的字符串。 for循环缓冲区是我构建每个字段并将其保存到我的类的地方。我已经在这里旋转了几天，任何帮助都会受到赞赏。
编辑：
以下是该程序正在阅读的文件中的内容： 0，Nicole 0，Debbie -
计划1
/*******************************************************\
* Debug Version 02-b-1 - string to string build *
* *
* Saving a Person Object to file *
* This program will have a class that can save and *
* retrieve itself to and from a flat file in cdf format *
* *
* The program will accept screen input for subsequent *
* Object store call and will allow a print command that *
* will create a file of mailing labels. *
\*******************************************************/
#include <cstdlib>
#include <iostream>
#include <string>
std::string current_person = "Why does this not work? "; // CDF String version of person record from file
std::string for_loop_buffer = " "; // the substring buffer
int counter2 = 0;
int main( )
{
for (int i = 0;i <= 23;++i){
/*****************************************************************************\
* This next line apears to be the problem *
\*****************************************************************************/
for_loop_buffer[counter2] = current_person[i];
std::cout << "DEBUG - Current person " << current_person << std::endl;
std::cout << "DEBUG - current Person element " << current_person[i] << std::endl;
std::cout << "DEBUG - for Loop Buffer " << for_loop_buffer << std::endl;
std::cout << "DEBUG - for Loop Buffer element " << for_loop_buffer[counter2] << std::endl;
std::cout << "DEBUG - for Loop Buffer counter " << counter2 << std::endl;
++counter2;
} // close for
return (0);
}
计划2
/*******************************************************\
* Debug Version 02 - Read data from a cdf file *
* *
* Saving a Person Object to file *
* This program will have a class that can save and *
* retrieve itself to and from a flat file in cdf format *
* *
* The program will accept screen input for subsequent *
* Object store call and will allow a print command that *
* will create a file of mailing labels. *
\*******************************************************/
#include <cstdlib>
#include <iostream>
#include <fstream>
#include <string>
#include <sstream>
using namespace std;
/***************************************************************\
* Class Definition - person *
* *
* Member functions *
* save_person -- Save the person object to a flat file in CDF *
* get_person -- Retrives a persons data from a CDF flat file *
\***************************************************************/
// Definition of the Class
class person_class {
public:
struct person_contact {
int person_number; // System assigned not on ui
std::string first_name;
};
// Declarations for the method Prototypes
public:
// A Function that retrieves 1 person from file and
// provides it to the user
void get_person();
} person;
/*********************************************************\
* person_class::get_person -- get a data record from file *
* *
\*********************************************************/
inline void person_class::get_person()
{
// Declaration of private variables for this method
std::string ui_first_name; // User Input from Keyboard
person_contact target_person; // Name of the opbect we are filling
std::string current_person; // CDF String version of person record from file
std::cout << "Enter the First Name of the person you are looking for: ";
std::cin >> ui_first_name;
std::cout << std::endl << "Matching Records: " << std::endl;
// Open file
std::ifstream input_file("ntc_db02test.ntc");
std::cout << "DEBUG - I opened the file " << std::endl;
current_person.clear();
while (input_file.good()){
std::cout << "DEBUG - I have entered the while loop " << std::endl;
// Grab the next record from a comma delimited file
getline(input_file,current_person);
std::cout << "DEBUG - I have performed a getline " << std::endl;
std::cout << current_person << std::endl;
// I need a mechanism to build substrings
// Substring Buffer stuff
int buffer_pointer = 0; // pointer to the next position in the substring buffer
std::string for_loop_buffer =" "; // the substring buffer
for_loop_buffer.clear();
int field_index = 0; // Which field is next to load
/*******************************************************************\
* If everything went as planned I have a single CDF person record *
* in the current_person string and now all I have to do is parse *
* it and place each field in the current instance. *
\*******************************************************************/
// load the instance with the record data from the file
for (int i = 0;i < current_person.length();++i){
std::cout << "DEBUG - I am in the for loop " << std::endl;
// look for the end of the CDF field
if(current_person[i] == ','){
// Write the buffer to the next field
std::cout << "DEBUG - I found a comma " << std::endl;
switch (field_index) {
case 0:
stringstream(for_loop_buffer) >> target_person.person_number;
std::cout << "DEBUG - Field Index " << field_index << std::endl;
std::cout << "DEBUG - For Loop Buffer " << for_loop_buffer << std::endl;
std::cout << "DEBUG - Person Number " << target_person.person_number << std::endl;
break;
case 1:
stringstream(for_loop_buffer) >> target_person.first_name;
std::cout << "DEBUG - First Name " << target_person.first_name << std::endl;
break;
default:
std::cout << "This should not happen, index not functioning " << '\n';
break;
} // Close Switch
// clear the buffer
for_loop_buffer.clear(); //SE
buffer_pointer = 0;
// set up the next field load - increment the field index
++field_index; //
}else{ // close if
std::cout << "DEBUG - not a comma " << std::endl;
// If the character is not a comma
// add the character to the buffer
/*****************************************************************************\
* !!!!!!!!!!!! This next line apears to be the problem !!!!!!!!!!!!!!! *
\*****************************************************************************/
for_loop_buffer[buffer_pointer] = current_person[i];
std::cout << "DEBUG - Primary Index i " << i << std::endl;
std::cout << "DEBUG - current Person element " << current_person[i] << std::endl;
std::cout << "DEBUG - Buffer Pointer " << buffer_pointer << std::endl;
std::cout << "DEBUG - for Loop Buffer element " << for_loop_buffer[buffer_pointer] << std::endl;
std::cout << "DEBUG - for Loop Buffer " << for_loop_buffer << std::endl;
// Increment the buffer pointer
++buffer_pointer;
} // close else
} // close for
if (target_person.first_name == ui_first_name){
// Code to print out full record
std::cout << target_person.first_name << " "
<< std::endl;
} // Close if
} // Close While
input_file.close();
} // Close Class
/******************************************************************************\
* The idea this time is to do as little in the main as possible and as much *
* in the class as is appropriate. So rather than read in data and pass it to *
* the method, I will call the method and let it do its own UI reading. *
\******************************************************************************/
int main( )
{
/**********************************************************\
* Ask the user if they want to Create a new person record *
* n or find a record in the database f *
\**********************************************************/
// Set up for user input
char command = 'f';
std::cout << " What do you want to do? New Person (n) or Find Person (f) ";
std::cin >> command;
while (command == 'n' || command == 'f'){
if (command == 'n'){
std::cout << "Do Nothing" << std::endl;
} else if (command == 'f'){
person_class current_person_object;
current_person_object.get_person();
}
command = 'x';
std::cout << "I am Back in Main" << std::endl;
}
std::cout << "You entered something other than a -n- or a -f-, program terminating now" << std::endl;
return (0);
}
答案 0 :(得分：3)
您正在循环遍历字符串，将其拆分为逗号，但是有标准库函数可以为您简化此操作。这听起来像家庭作业，所以我不会发布任何代码答案，但这里有一些提示：
std::string::find_first_of将为您搜索字符串，并告诉您下一个逗号的位置。std::string::substr给定字符串中的位置和长度，将返回字符串的一部分。在循环中使用上述两个函数，您可以用更少的代码选择字段，这样更容易理解。
或者，可以直接从流中读取值，因为您使用的std::getline函数有一个额外的参数来指定哪个字符终止该行（即逗号）。
答案 1 :(得分：2)
难以看清代码，但在您的“真实”代码中，您说for_loop_buffer.clear();，这是for_loop_buffer = "";的同义词，后来我认为您正在访问该成员（现在为空）字符串：
for_loop_buffer[buffer_pointer] = current_person[i]; // Illegal access!