我正在尝试为一个简单的外壳实现历史功能。历史记录应保存最近执行的 10 个命令。我将代码放在下面，但是遇到了一些问题。
首先，当我输入一个（或两个）命令并键入history以显示历史记录时，不会显示任何内容。但是，当我再输入几个命令时，将显示整个历史记录（就像它应该的那样），但每个历史记录索引旁边会显示一串零。
做错了什么，我该如何解决这个问题？
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#define MAX_LINE 80 /* 80 chars per line, per command, should be enough. */
char *history[10][MAX_LINE];
int placePointer;
/**
* setup() reads in the next command line, separating it into distinct tokens
* using whitespace as delimiters. setup() sets the args parameter as a
* null-terminated string.
*/
void setup(char inputBuffer[], char *args[],int *background)
{
int length, /* # of characters in the command line */
i, /* loop index for accessing inputBuffer array */
start, /* index where beginning of next command parameter is */
ct; /* index of where to place the next parameter into args[] */
ct = 0;
/* read what the user enters on the command line */
length = read(STDIN_FILENO, inputBuffer, MAX_LINE);
start = -1;
if (length == 0)
exit(0); /* ^d was entered, end of user command stream */
if (length < 0){
perror("error reading the command");
exit(-1); /* terminate with error code of -1 */
}
/* examine every character in the inputBuffer */
for (i = 0; i < length; i++) {
switch (inputBuffer[i]){
case ' ':
case 't' : /* argument separators */
if(start != -1){
args[ct] = &inputBuffer[start]; /* set up pointer */
ct++;
}
inputBuffer[i] = ' '; /* add a null char; make a C string */
start = -1;
break;
case 'n': /* should be the final char examined */
if (start != -1){
args[ct] = &inputBuffer[start];
ct++;
}
inputBuffer[i] = ' ';
args[ct] = NULL; /* no more arguments to this command */
break;
case '&':
*background = 1;
inputBuffer[i] = ' ';
break;
default : /* some other character */
if (start == -1)
start = i;
}
}
args[ct] = NULL; /* just in case the input line was > 80 */
}
void displayHistory(){
printf("Display History:n");
int i = placePointer;
int j;
int counter;
while(counter < 10) {
printf("%d: ",counter);
for (j = 0; j < MAX_LINE; j++) {
printf("%d",history[i][j]);
}
printf("n");
i = (i + 1) % 10;
counter++;
}
}
/*
void runHistoryAt(int index){
printf("Run History At:n");
char *arg1 = &history[placePointer + index][0];
char *argLine[MAX_LINE/2+1];
int j;
for (j = 0; j < MAX_LINE/2+1; j++) {
*argLine[j] = history[placePointer + index][j];
}
execvp(arg1,argLine);
}*/
int main(void)
{
char inputBuffer[MAX_LINE]; /* buffer to hold the command entered */
int background; /* equals 1 if a command is followed by '&' */
char *args[MAX_LINE/2+1];/* command line (of 80) has max of 40 arguments */
while (1){ /* Program terminates normally inside setup */
background = 0;
printf("COMMAND->");
fflush(0);
setup(inputBuffer, args, &background); /* get next command */
/* the steps are:
(1) fork a child process using fork()
(2) the child process will invoke execvp()
(3) if background == 0, the parent will wait,
otherwise returns to the setup() function. */
pid_t pid = fork();
printf("Fork created.n");
if(pid < 0){
printf("Fork failed.n");
}else if(pid == 0){
if( strcmp(args[0],"history") == 0){ /* Print History */
displayHistory();
}else if(strcmp(args[0],"r") == 0){ /* r num */
int index = (int) args[1];
/*runHistoryAt( index - 1);*/
}else if(strcmp(args[0],"rr") == 0){ /* Run recent */
/*runHistoryAt(0);*/
}else{ /* Execute normally */
printf("executing..., adding to history buffern");
/* Add args to history buffer */
int j;
for (j = 0; j < sizeof(args); j++) {
history[placePointer][j] = args[j];
}
placePointer = (placePointer + 1) % 10;
/* Execute! */
execvp(args[0],args);
}
}
if(background == 0){
wait(NULL);
}else{
setup(inputBuffer, args, &background);
}
}
}
所有args指针都是指向inputBuffer的指针，其中包含最近输入的输入行。 因此，当您将args保存到history时，您只是保存指针，而不是实际指向字符串，字符串仍然（仅）在inputBuffer中。 当您阅读下一个命令时，它会覆盖inputBuffer，使所有保存的history指针无效 - 它们现在指向当前命令的某个部分，而不是旧命令。