如何对文件中的数据进行操作？
本帖最后由 瑶瑶无期 于 2021-4-24 17:26 编辑我的文本文件是图中这样的俩列数据，第一列是X，第二列是Y，输入任意连续X，得出最接近的Y，如输入0.05，得出17.0，输入0.23，得出16.6.请问怎么实现？数据大概四百行。 本帖最后由 yuxijian2020 于 2021-4-25 17:17 编辑
不知道你用的是c还是c++
c语言:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#define MAX_LEN 500
typedef struct _Pair
{
double key;
double value;
} Pair;
const Pair errorPair = { -0.1, -0.1 };
//分割字符串
Pair StringSplit(char* str, char sep)
{
int pos = -1;
for (int i = 0; i < strlen(str); i++)
{
if (sep == str)
{
pos = i;
break;
}
}
if (pos == -1)
return errorPair;
int headLen = pos + 1;
int tailLen = strlen(str) - pos - 1;
char* front = (char*)malloc(headLen + 1);
char* back = (char*)malloc(tailLen + 1);
if (!front || !back)
return errorPair;
memset(front, 0, headLen + 1);
memset(back, 0, tailLen + 1);
memcpy(front, str, headLen);
front = '\0';
memcpy(back, str + headLen, tailLen);
back = '\0';
Pair result = { 0.0, 0.0 };
result.key = atof(front);
result.value = atof(back);
free(front);
free(back);
return result;
}
//读取文件内容,函数返回值需要free
char* ReadFile(const char* path)
{
FILE* file;
fopen_s(&file, path, "r");
if (!file)
return NULL;
fseek(file, 0, SEEK_END);
int length = ftell(file);
fseek(file, 0, SEEK_SET);
char* content = (char*)malloc(length);
if (!content)
return NULL;
fread(content, sizeof(char), length, file);
return content;
}
//返回一个申请空间的Pair指针，此函数调用后，需要free返回值
Pair* StringToPair(const char* str)
{
Pair* result = (Pair*)malloc(MAX_LEN * sizeof(Pair));
if (!result)
return NULL;
memset(result, 0, MAX_LEN * sizeof(Pair));
int start = 0;
int cur = 0;
int size = strlen(str);
for (int i = 0; i < size; i++)
{
if (str == '\n')
{
char* temp = (char*)malloc(i - start + 1);
if (!temp)
{
free(result);
return NULL;
}
memset(temp, 0, i - start + 1);
memcpy(temp, str + start, i - start);
temp = '\0';
Pair p = StringSplit(temp, '\t');
result.key = p.key;
result.value = p.value;
cur++;
start = i + 1;
free(temp);
}
}
return result;
}
double FindLike(Pair* pairs, double tar)
{
double min = 1000000.0;
double cur = 0.0;
Pair like = { 0.0, 0.0 };
for (int i = 0; i < MAX_LEN; i++)
{
cur = fabs(pairs.key - tar);
if (cur < min)
{
like.key = pairs.key;
like.value = pairs.value;
min = cur;
}
}
return like.value;
}
int main()
{
char path[] = "data.txt";
char* content = ReadFile(path);
Pair* pairs = StringToPair(content);
free(content);
double in = 0.0;
printf_s("请输入一个小数:");
scanf_s("%lf", &in);
double result = FindLike(pairs, in);
free(pairs);
printf_s("%.1lf\n", result);
return 0;
}
c++:
#include<iostream>
#include <fstream>
#include<string>
#include <vector>
using namespace std;
//按sep分割字符串，并转化为2个double类型组成的pair
pair<double, double> StringSplit(const string& str, const string& sep)
{
size_t pos = str.find(sep);
if (pos == string::npos)
return pair<double, double>();
string front;
string back;
front.assign(str, 0, pos);
back.assign(str, pos + sep.size(), str.size() - pos - sep.size());
double first = atof(front.c_str());
double second = atof(back.c_str());
return make_pair(first, second);
}
//读取文件并将文件内容转为 2个double类型组成的pair 的数组
//数组元素为double 和 double 组成的pair
vector<pair<double, double>> ReadFileToVector(const string& path)
{
fstream file(path, ios::in);
vector<pair<double, double>> dataPairs;
string line;
while (getline(file, line))
dataPairs.emplace_back(StringSplit(line, "\t"));
return dataPairs;
}
//获取用户输入，并输出
void GetInputAndPrint()
{
//这里ReadFileToVector方法的参数是文件路径
vector<pair<double, double>> data(ReadFileToVector("data.txt"));
double in;
printf_s("请输入一个小数:");
cin >> in;
pair<double, double> like;
double min = 1000000.0;
double cur = 0.0;
//遍历数组找到最接近的值
for (const auto& p : data)
{
cur = fabs(p.first - in);
if (cur < min)
{
like = p;
min = cur;
}
}
printf_s("%.1lf\n", like.second);
}
int main()
{
GetInputAndPrint();
return 0;
}
楼上代码知识点比效深，给你搞个简单的。
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int GetSplitIndex(char buf[])
{
int i;
i=0;
while(buf!=9 && buf!=32)
{
i++;
}
return i;
}
double GetResult(double num, double c1[], double c2[])
{
int i;
double current = 0.0, min=1000000.0, tmp = -1;
i=0;
while( c2 != 0)
{
current = fabs(c1 - num);
if(current<min)
{
tmp = c2;
min = current;
}
i++;
}
return tmp;
}
int main()
{
FILE *fp = NULL;
double c1={0}, c2={0}, in;
char buf = {'\0'};
int i, index;
// 读取文件 把第一列保存在c1 第二列保存在c2
fp = fopen("D:\\Users\\Administrator\\Desktop\\ctest\\Debug\\readme.txt", "r");
if(fp==NULL)
{
printf("文件打开失败~！\n");
return 0;
}
i = 0;
while( fgets(buf, 255, fp) != NULL )
{
index = GetSplitIndex(buf); // 取得 2列中间 以 TABLE 或 空格 分割符的第一次出现的位置
buf = '\0';
c1 = atof(buf); // 把字符串转为double保存起来
c2 = atof(&buf); // 把字符串转为double保存起来
i++;
}
fclose(fp);
// 循环获取用户输入
while(scanf("%lf", &in)!=0) // 输入非数字 退出
{
printf("%f\n", GetResult(in, c1, c2));
}
return 0;
}
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