c - 如何在 c/gcc 中返回脚本？

Question

自从我用 C 编写最后一行以来已经有好几年了，现在我正试图重新开始制作一些功能并将其用作 php 的扩展。

这是一个创建“小网址”的简单函数

让我们说:

a0bga0bfa0bh

我遇到的问题是，当我必须“递增”像 zzz 这样的字符串时，我得到了:总线错误

否则，如果我递增 abr，我得到的结果是:abs

有时我认为我的问题是返回字符串结果

这两个代码都可以正常使用，因为我将它们发布在这里。

编译我正在使用:gcc append_id_test.c -o append_id

我在 OS X 豹

当我这样做时，它起作用了:(请注意对函数 append_id 的调用)

#include <stdlib.h>
#include <string.h>
#include <stdio.h>

char* append_id(char*);
int main(void) {
    char *x;
    char *incremented;

    x = "aaab";

    printf("%s\n", append_id(x)); // should print 00000 (lenght 5)


    incremented = (char *) malloc((strlen(x) + 2) * sizeof(char));
    incremented = append_id(x);

    printf("--->  %s\n", incremented); // should print 00000 (lenght 5)

}

char* append_id(char *id) {

    int x;
    char* new_id;
    int id_size = strlen(id);

    new_id = (char *) malloc((strlen(id) + 2) * sizeof(char));

    for ( x = 0; x < id_size; x++ )
    {
        new_id[x] = '0';
    }

    strcat(new_id, "0");

    return new_id;
}

但整个代码无法正常工作(如您所见，对 append_id 函数的调用与上述示例的调用方式相同)

#include <stdlib.h>
#include <string.h>
#include <stdio.h>


char* append_id(char*);
char* increment_id(char*, int);
char* get_next_id(char*);


int main(int argc, char *argv[]) {
    char *x;
    int a;

    x = "zz";

    printf("incrementando %s -> %s\n", "zz", get_next_id(x));

    return 0;
}


char * get_next_id(char *last_id)
{ 
    int x, pos;
    char *next_id;
    char is_alnum = 1;

    // if the last id is -1 (non-existant), start at the begining with 0
    if ( strlen(last_id) == 0 )
    {
        next_id = "0";
    }
    else
    {

        // check the input
        for(x = 0; last_id[x]; x++) 
        {
            if(!isalnum(last_id[x]))
            {
                is_alnum = 0;
                break;
            }
        }

        if (is_alnum == 0)
        {
            return "";
        }


        // all chars to lowercase
        for(x = 0; last_id[x]; x++) 
        {
            last_id[x] = tolower(last_id[x]);
        }


        // loop through the id string until we find a character to increment
        for ( x = 1; x <= strlen(last_id); x++ )
        {
            pos = strlen(last_id) - x;

            if ( last_id[pos] != 'z' )
            {
                next_id = increment_id(last_id, pos);
                break; // <- kill the for loop once we've found our char
            }
        }

        // if every character was already at its max value (z),
        // append another character to the string
        if ( strlen(next_id) == 0)
        {
            next_id = (char *) malloc((strlen(last_id) + 2) * sizeof(char));
            next_id = append_id(last_id);
        }

    }


    return next_id;
}



char* append_id(char *id) {

    int x;
    char* new_id;
    int id_size = strlen(id);

    new_id = (char *) malloc((strlen(id) + 2) * sizeof(char));

    for ( x = 0; x < id_size; x++ )
    {
        new_id[x] = '0';
    }

    strcat(new_id, "0");

    return new_id;
}



char* increment_id(char *id, int pos){
    char current, new_char;
    char * new_id ;
    int x;

    new_id = (char *) malloc((strlen(id) + 1) * sizeof(char));


    current = id[pos];

    if ( current >= 0x30 && current <= 0x39 )
    {
        if ( current < 0x39 )
        {
            new_char = current + 1;
        }
        else // if we're at 9, it's time to move to the alphabet
        {
            new_char = 'a';
        }
    }
    else // move it up the alphabet
    {
        new_char = current + 1;
    }


    for ( x = 0; x < strlen(id); x++ )
    {
        if (x == pos) {
            new_id[x] = new_char;
        }
        else {
            new_id[x] = id[x];
        }
    }


    // set all characters after the one we're modifying to 0
    if ( pos != (strlen(new_id) - 1) )
    {
        for ( x = (pos + 1); x < strlen(new_id); x++ )
        {
            new_id[x] = '0';
        }
    }

    return new_id;
}

Answer 1

下次请使用 -Wall 编译 ;)

首先，在使用 tolower 和 isalnum 之前，

#include <ctype.h>

其次，您将 x(在 main 作用域中)指定为指向一个字符串文字，它是 const。因此，当您尝试在小写时覆盖它时，您会遇到内存冲突。尝试初始化，比如说，

char x[] = "zz";

您还应该在 get_next_id 中初始化 next_id:

char *next_id = NULL;

稍后，不要在空指针上运行 strlen:

// if every character was already at its max value (z),
// append another character to the string
if (!next_id || !strlen(next_id))
{
    next_id = append_id(last_id);
}

在append_id中，使用strcat前需要先null终止:

for ( x = 0; x < id_size; x++ )
{
    new_id[x] = '0';
}
new_id[id_size] = 0;

这样就可以正常工作了。您的代码有很多错误。你提到

had been years since I wrote my last line in C

我真的希望你多年前就对它有了更好的理解，看来你对很多基本的 C 内存、字符串和指针概念一无所知。