搜索记录集/更新值 [英] search in record set / update value
问题描述
我使用结构,向量创建了一个记录集,并添加了几对记录。这是执行此操作的代码。
I created a record set using structs, vector and added couple of records. This is the code that does it. This should run as is - on an Arduino/ESP8266/ESP32.
#include <string>
#include <vector>
struct student {
std::string studentName; // I only load this once at startup. So can be const
std::string studentSlot; // <= This should be updateable
bool wasPresent; // <= This should be updateable
student(const char* stName, const char* stSlot, bool stPresent) :
studentName(stName),
studentSlot(stSlot),
wasPresent(stPresent)
{}
};
std::vector<student> studentRecs;
void setup() {
delay(1000);
Serial.begin(115200);
// Add couple of records
student record1("K.Reeves", "SLT-AM-03", false);
student record2("J.Wick", "SLT-PM-01", true);
studentRecs.push_back(record1);
studentRecs.push_back(record2);
}
void loop() {
Serial.println();
// Get the size
int dsize = static_cast<int>(studentRecs.size());
// Loop, print the records
for (int i = 0; i < dsize; ++i) {
Serial.print(studentRecs[i].studentName.c_str());
Serial.print(" ");
Serial.print(studentRecs[i].studentSlot.c_str());
Serial.print(" ");
Serial.println(String(studentRecs[i].wasPresent));
}
// Add a delay, continue with the loop()
delay(5000);
}
我能够使用for循环读取单个记录。我不确定这是否是最好的方法,但确实可以。
I am able to read the individual records using the for loop. I am not sure if it's the best way but it does work.
我需要能够在此记录集上做几件事。
I need to be able to do couple of things on this record set.
1)搜索/查找 studentName
的记录。我可以通过循环找到它,但是这对我来说效率低下又难看。
1) Search/find a record by studentName
. I can find it by looping but that comes across as inefficient+ugly to me.
2)能够更新 studentSlot
和 wasPresent
通过一些研究和实验,我发现我可以这样做来更改 wasPresent
With some research and experimentation I found that I could do this to change wasPresent
studentRecs[0].wasPresent = false;
同样,我不确定这是否是最好的方法,但它是否有效。我希望能够更改 studentSlot
,但我对此不确定,因为这是我第一次处理结构和向量。 studentName是恒定的(我只需要在启动时加载一次),即可在运行时更改studentSlot。我不确定该如何更改。可能需要我删除const char *,执行一些strcpy的操作或其他操作,但是我仍然坚持这样做。简而言之,有3件事我需要一点帮助
Again I am not sure if that is the best way but it works. I want to be able to change studentSlot
and I am not sure about that as this is my first time dealing with structs and vector. The studentName is constant ( I only need to load it once at startup ) where the studentSlot can change during runtime. I am not sure how to change that. It may need me to remove the const char*, do some strcpy thingy or something but I am stuck at that. In short there are 3 things I need a little help on
1)按学生姓名搜索/查找记录
1) Search/find a record by studentName
2)能够更新studentSlot
2) Be able to update studentSlot
3)删除所有记录。 注意:我刚刚发现 studentRecs.clear()
会这样做
3) Delete all the records. Note: I just figured out that studentRecs.clear()
does this
I我不确定我是否能够足够清楚地解释这一点。因此,如有任何疑问,请射击。谢谢。
I am not sure if I have been able to explain this clearly enough. So any questions please shoot. Thanks.
推荐答案
好吧,我认为您最好的选择是来
循环以搜索 studentName
。取决于您使用的C ++版本:
Well, I think your best bet is to go with for
loop to search for studentName
. Depending on what C++ revision you are using:
student searchForName(const std::string & name)
{
for (auto item : studentRecs)
{
if (item.studentName == name)
return item;
}
return student();
}
或者如果您限于C ++ 11之前的版本:
or if you are constrained to pre-C++11:
student searchForName(const std::string & name)
{
for (std::size_t cnt = 0; cnt < studentRecs.size(); ++cnt)
{
if (studentRecs[cnt].studentName == name)
return item;
}
return student();
}
其余的非常相似。
BTW .:您可以更改:
BTW.: You can change:
...
// Get the size
int dsize = static_cast<int>(studentRecs.size());
// Loop, print the records
for (int i = 0; i < dsize; ++i) {
...
到:
...
// Loop, print the records
for (std::size_t i = 0; i < studentRecs.size(); ++i) {
...
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