c++ - strcpy 可以在 Arduino 上自行编辑内存地址吗?
问题描述
我正在从串行总线解析 char 数组并将它们的内容复制到全局数组中以便处理到其他函数中。当我反复使用时strcpy()
,我注意到奇怪的行为。strtok()
使用 Arduino Mega,可以重复调用strcpy
破坏内存地址吗?
这适用于低级仪器,让 Arduino 作为本地微控制器通过串行接收命令。我已经完成了几种不同的初始化全局数组的方法,包括:
//char testDate = "YYmmDD"; //failed
//char testDate[6] = "";
//char testDate[6] = "YYmmDD";
//char testDate[6] = {'Y', 'Y', 'm', 'm', 'D', 'D'};
//char testTime = "HHMMSS"; //failed
//char testTime[6] = "";
//char testTime[6] = "HHMMSS";
//char testTime[6] = {'H', 'H', 'M', 'M', 'S', 'S'};
//char logfile[24] = "BATCH_YYmmDD_HHMMSS$.txt"; // 20 + 4, exact size
//char logfile[24] = {' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' '};
//char testDate[6] = ""; // Null
//char testTime[6] = ""; // Null
char testDate[6] = {'Y', 'Y', 'm', 'm', 'D', 'D'};
char testTime[6] = {'H', 'H', 'M', 'M', 'S', 'S'}; // is appending?
char logfile[24] = ""; // Null
演示代码,最简单的形式;
#include <String.h>
char gva_logfile[24] = {' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' '};
char gva_testDate[6] = {'Y', 'Y', 'm', 'm', 'D', 'D'}; // is appending?
char gva_testTime[6] = {'H', 'H', 'M', 'M', 'S', 'S'};
char lva_testDate[6];
//String y = "BATCH|190117;151442$";
//int lan = y.length(); // should be 20
char x[20] = "BATCH|190117;151442$";
int lan = strlen(x);
//y.toCharArray(x, lan);
//strcpy(x, y);
//y.toCharArray(x, 20);
//strcpy(x, "BATCH|190117;151442$");
void setup() {
// put your setup code here, to run once:
Serial.begin(9600);
Serial.print("<");
for(int i=0; i<6; i++){
Serial.print(gva_testDate[i]); // works
//Serial.print(gva_testTime[i]); // works
}
Serial.println(">");
}
void loop() {
// put your main code here, to run repeatedly:
char tele[6] = {' ', ' ', ' ', ' ', ' ', ' '};
while(1){
char flarb[lan];
strcpy(flarb, x);
//Serial.println(flarb);
if(strstr(flarb, "BATCH|")){
char * strtokIndx;
strtokIndx = strtok(x, "|");
//strcpy(tele, strtokIndx); // did nothing?
strtokIndx = strtok(NULL, ";");
strcpy(gva_testDate, strtokIndx); // missing?
Serial.println(gva_testDate); // Not missing
for(int i=0; i<6; i++){
lva_testDate[i] = gva_testDate[i];
}
strtokIndx = strtok(NULL, "$");
strcpy(gva_testTime, strtokIndx); // is fine...
Serial.println(gva_testDate); // MISSING
Serial.println(lva_testDate);
if(strstr(gva_testDate, "YYmmDD")!=NULL || strstr(gva_testTime, "HHMMSS")!=NULL){
//if((gva_testDate == "YYmmDD") || (gva_testTime == "HHMMSS")){
char io[28]; // 16 + 2*6
sprintf(io, "063 ERROR: %s,%s", gva_testDate, gva_testTime);
//logArdData(io);
Serial.print("<");
Serial.print(io);
Serial.println(">");
Serial.flush();
}
//else if((strstr(gva_testDate, "YYmmDD") && strstr(gva_testTime, "HHMMSS"))==NULL){
else if((strstr(gva_testDate, "YYmmDD")==NULL && strstr(gva_testTime, "HHMMSS")==NULL)){
//else if((gva_testDate != "YYmmDD") && (gva_testTime != "HHMMSS")){
char io[26]; // 14 + 2*6
//sendArdData(gva_testDate); // is combinined?
//sendArdData(gva_testTime); // still itself
sprintf(io, "Assigned %s,%s", gva_testDate, gva_testTime); // is combining testDate and testTime, then printing testTime?
Serial.print("<");
Serial.print(io);
Serial.println(">");
//sendArdData(io);
//logArdData(io);
Serial.flush();
}
}
}
}
当我尝试重新打印gva_testDate
分配后的存储值时gva_testTime
,不知何故gva_testDate
变成NULL
了190117
. 我预计这gva_testDate
将保留其新分配的值,但情况似乎并非如此。
strcpy()
http://www.cplusplus.com/reference/cstring/strcpy/?kw=strcpy和strtok()
http://www.cplusplus.com/reference/cstring/strtok/的 C++ 参考页面没有提到内存损坏问题/警告,所以我不希望重复调用会修改原始字符串x
或解析的字符数组gva_testDate
& gva_testTime
。
解决方案
我做了一个测试,并确切地发现了这里发生的事情。
这是 strtok 的问题,也是您为所有这些字符串函数提供字符数组而没有字符串分隔符空间的事实,即“0”。
这是我在电脑上写的用来测试东西的测试函数
void printAllObjects(int location,char *x, char* strtokIndx, char *gva_testDate,char *gva_testTime)
{
printf("At location %d\n x pointer %d, string %s\n"
" strtokIndx pointer %d, string %s\n "
"gva_testDate pointer %d, string %s\n "
"gva_testTime pointer %d, string %s\n ",location,x,x,strtokIndx,strtokIndx,gva_testDate,gva_testDate,gva_testTime,gva_testTime);
}
然后我将你所有的 arduino 代码复制到我的计算机上,注释掉所有串行命令,添加 stdio 头文件,并在多个位置使用上述功能。
#include <cstdlib>
#include <String.h>
#include <stdio.h>
using namespace std;
/*
*
*/
char gva_logfile[24] = {' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' '};
char gva_testDate[6] = {'Y', 'Y', 'm', 'm', 'D', 'D'}; // is appending?
char gva_testTime[6] = {'H', 'H', 'M', 'M', 'S', 'S'};
char lva_testDate[6];
//String y = "BATCH|190117;151442$";
//int lan = y.length(); // should be 20
char x[] = "BATCH|190117;151442$";
int lan = strlen(x);
//y.toCharArray(x, lan);
//strcpy(x, y);
//y.toCharArray(x, 20);
//strcpy(x, "BATCH|190117;151442$");
void printAllObjects(int location,char *x, char* strtokIndx, char *gva_testDate,char *gva_testTime)
{
printf("At location %d\n x pointer %d, string %s\n"
" strtokIndx pointer %d, string %s\n "
"gva_testDate pointer %d, string %s\n "
"gva_testTime pointer %d, string %s\n ",location,x,x,strtokIndx,strtokIndx,gva_testDate,gva_testDate,gva_testTime,gva_testTime);
}
void setup() {
// put your setup code here, to run once:
// Serial.begin(9600);
//
// Serial.print("<");
// for(int i=0; i<6; i++){
// Serial.print(gva_testDate[i]); // works
// //Serial.print(gva_testTime[i]); // works
// }
// Serial.println(">");
}
void loop() {
// put your main code here, to run repeatedly:
char tele[6] = {' ', ' ', ' ', ' ', ' ', ' '};
while(1){
char flarb[lan];
strcpy(flarb, x);
//Serial.println(flarb);
if(strstr(flarb, "BATCH|")){
char * strtokIndx;
printAllObjects(1,x,strtokIndx,gva_testDate,gva_testTime);
strtokIndx = strtok(x, "|");
printAllObjects(2,x,strtokIndx,gva_testDate,gva_testTime);
//strcpy(tele, strtokIndx); // did nothing?
strtokIndx = strtok(NULL, ";");
printAllObjects(3,x,strtokIndx,gva_testDate,gva_testTime);
strcpy(gva_testDate, strtokIndx); // missing?
printAllObjects(4,x,strtokIndx,gva_testDate,gva_testTime);
// Serial.println(gva_testDate); // Not missing
for(int i=0; i<6; i++){
lva_testDate[i] = gva_testDate[i];
}
strtokIndx = strtok(NULL, "$");
printAllObjects(5,x,strtokIndx,gva_testDate,gva_testTime);
strcpy(gva_testTime, strtokIndx); // is fine...
printAllObjects(6,x,strtokIndx,gva_testDate,gva_testTime);
// Serial.println(gva_testDate); // MISSING
// Serial.println(lva_testDate);
if(strstr(gva_testDate, "YYmmDD")!=NULL || strstr(gva_testTime, "HHMMSS")!=NULL){
//if((gva_testDate == "YYmmDD") || (gva_testTime == "HHMMSS")){
char io[28]; // 16 + 2*6
sprintf(io, "063 ERROR: %s,%s", gva_testDate, gva_testTime);
//logArdData(io);
// Serial.print("<");
// Serial.print(io);
// Serial.println(">");
// Serial.flush();
}
//else if((strstr(gva_testDate, "YYmmDD") && strstr(gva_testTime, "HHMMSS"))==NULL){
else if((strstr(gva_testDate, "YYmmDD")==NULL && strstr(gva_testTime, "HHMMSS")==NULL)){
//else if((gva_testDate != "YYmmDD") && (gva_testTime != "HHMMSS")){
char io[26]; // 14 + 2*6
//sendArdData(gva_testDate); // is combinined?
//sendArdData(gva_testTime); // still itself
sprintf(io, "Assigned %s,%s", gva_testDate, gva_testTime); // is combining testDate and testTime, then printing testTime?
// Serial.print("<");
// Serial.print(io);
// Serial.println(">");
//sendArdData(io);
//logArdData(io);
// Serial.flush();
}
}
}
}
int main(int argc, char** argv) {
setup();
printf("Entering loop\n");
loop();
return 0;
}
这是我得到的输出
Entering loop
At location 1
x pointer 199946368, string BATCH|190117;151442$
strtokIndx pointer 0, string (null)
gva_testDate pointer 199946344, string YYmmDDHHMMSS
gva_testTime pointer 199946350, string HHMMSS
At location 2
x pointer 199946368, string BATCH
strtokIndx pointer 199946368, string BATCH
gva_testDate pointer 199946344, string YYmmDDHHMMSS
gva_testTime pointer 199946350, string HHMMSS
At location 3
x pointer 199946368, string BATCH
strtokIndx pointer 199946374, string 190117
gva_testDate pointer 199946344, string YYmmDDHHMMSS
gva_testTime pointer 199946350, string HHMMSS
At location 4
x pointer 199946368, string BATCH
strtokIndx pointer 199946374, string 190117
gva_testDate pointer 199946344, string 190117
gva_testTime pointer 199946350, string
At location 5
x pointer 199946368, string BATCH
strtokIndx pointer 199946381, string 151442
gva_testDate pointer 199946344, string 190117
gva_testTime pointer 199946350, string
At location 6
x pointer 199946368, string BATCH
strtokIndx pointer 199946381, string 151442
gva_testDate pointer 199946344, string 190117151442
gva_testTime pointer 199946350, string 151442
基于这些数据,这是我的结论。
strtok 函数修改原始字符串并将搜索字符替换为 null,然后将字符串复制到新索引并返回索引。
strcpy 没有对您的代码做任何事情,您已经以这样的方式编写缓冲区值,以至于 strcpy 似乎在做令人讨厌的事情,但它只是在做它应该做的事情。复制字符串直到找到空值。在大多数情况下,它会给您带来很多麻烦,但在这种特定情况下不会。
从结果中可以看出,gva_testDate 和 gva_testTime 的指针差为 6,因此当 gva_testTime 被填充时,如果您使用 gva_testDate 作为字符串,则仅在 12 个字符的末尾看到空值。
lva_testDate 也应该是你的缓冲区,你需要给它一个开始的值,否则它会变成一个空缓冲区,最终可能会根据代码编译的内容修改不同的东西。
为了解决这个问题,我初始化了所有变量,输出打印在下面。
char gva_testDate[] = "YYmmDD"; // is appending?
char gva_testTime[] = "HHMMSS";
char lva_testDate[20];
//String y = "BATCH|190117;151442$";
//int lan = y.length(); // should be 20
char x[] = "BATCH|190117;151442$";
int lan = strlen(x);
输出
Entering loop
At location 1
x pointer 107077760, string BATCH|190117;151442$
strtokIndx pointer 0, string (null)
gva_testDate pointer 107077736, string YYmmDD
gva_testTime pointer 107077743, string HHMMSS
At location 2
x pointer 107077760, string BATCH
strtokIndx pointer 107077760, string BATCH
gva_testDate pointer 107077736, string YYmmDD
gva_testTime pointer 107077743, string HHMMSS
At location 3
x pointer 107077760, string BATCH
strtokIndx pointer 107077766, string 190117
gva_testDate pointer 107077736, string YYmmDD
gva_testTime pointer 107077743, string HHMMSS
At location 4
x pointer 107077760, string BATCH
strtokIndx pointer 107077766, string 190117
gva_testDate pointer 107077736, string 190117
gva_testTime pointer 107077743, string HHMMSS
At location 5
x pointer 107077760, string BATCH
strtokIndx pointer 107077773, string 151442
gva_testDate pointer 107077736, string 190117
gva_testTime pointer 107077743, string HHMMSS
At location 6
x pointer 107077760, string BATCH
strtokIndx pointer 107077773, string 151442
gva_testDate pointer 107077736, string 190117
gva_testTime pointer 107077743, string 151442
我希望这有帮助。
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