分段错误（核心转储）

Question

I'm trying to receive 9 float data using UART, every float is sent in the form XXX.XX. So I'm going to receive 5*9 =45 informations.

I tried to make the data received in a array of 45 char then I can do what I want with this array, but I get this famous error when i run my application : Segmentation fault (core dumped )

my code is

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <stdio.h>
#include <string>
#include <string.h>
#include <errno.h>
#include <wiringSerial.h>
using namespace std;
int main (){
    int fd;
    float courant;
    float voltage;
    float activepower;
    float reactivepower;
    float apparentpower;
    float powerfactor;
    float frequency;
    float temperature;
    float indexIns;
    string courantC;
    string voltageC;
    string activepowerC;
    string reactivepowerC;
    string apparentpowerC;
    string powerfactorC;
    string frequencyC;
    string temperatureC;
    string indexinsC;

    char receivedData[45];
    int i=0;
    if ((fd = serialOpen("/dev/ttyS1",9600)) < 0)
    {
        fprintf(stderr,"Unable to open serial device %s\n",strerror(errno));
        return 1;
    }
    // Loop , getting and printing characters

    for (int j=0; j<45; j++)
    {
        i = serialGetchar(fd);
        receivedData[j] = char(i);

        if (j = 44) {
            j = 0;

            courantC = receivedData[0]+receivedData[1]+receivedData[2]+"." + receivedData[3]+receivedData[4];
            voltageC = receivedData[5]+receivedData[6]+receivedData[7]+"." + receivedData[8]+receivedData[9];
            activepowerC = receivedData[10]+receivedData[11]+receivedData[12]+"." + receivedData[13]+receivedData[14];
            reactivepowerC = receivedData[15]+receivedData[16]+receivedData[17]+"." + receivedData[18]+receivedData[19];
            apparentpowerC = receivedData[20]+receivedData[21]+receivedData[22]+"." + receivedData[23]+receivedData[24];
            powerfactorC = receivedData[25]+receivedData[26]+receivedData[27]+"." + receivedData[28]+receivedData[29];
            frequencyC = receivedData[30]+receivedData[31]+receivedData[32]+"." + receivedData[33]+receivedData[34];
            temperatureC = receivedData[35]+receivedData[36]+receivedData[37]+"." + receivedData[38]+receivedData[39];
            indexinsC = receivedData[40]+receivedData[41]+receivedData[42]+"." + receivedData[43]+receivedData[44];

           
        }
        printf("a=%c ", char(i));

        fflush(stdout);

The command used to compile

gcc receiveData.cpp -o receiveData -lwiringPi -lpthread -lstdc++

Answer 1

This line:

courantC = receivedData[0]+receivedData[1]+receivedData[2]+"." + receivedData[3]+receivedData[4];

causes undefined behavior (UB) and is probably the cause of the segment fault. In this line you have an array of char , this here "." , with 2 chars, '.' and '\\0' . This array is stored somewhere. When you use it like this it decays to a pointer that points at the start of the array. The rest are all char , which are integers in C. They are added together and added to the pointer pointing to the array "." . This pointer then points to some unknown memory region which is accessed by the String class to be copied to courantC . But accessing the region causes UB.