扫描多字串扫描

Question

我想用sscanf捕获以下c#中的字符串

"1=Salam Khobi|FC93F8A120F491F3A8=Rial|F191FEA4"

但是scan只使用"Salam“填充&customInput.type和customInputTitle[0]，而字符串的其他部分则不会扫描。

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

typedef enum {
    INPUT_NUMBER = 0,
    INPUT_NORMAL = 1,
    INPUT_PASSWORD = 2,
    INPUT_PAYAMOUNT = 3,
} inputType;

typedef struct {
    char * title[2];
    char * extra[2];
    inputType type;
    unsigned minLen:6;
    unsigned maxLen:6;
    unsigned forceLen:1;
    unsigned editable:1;
    unsigned char data[100];
} lcdInput;
#define CUSTOM_INPUT_LENGTH     40
static unsigned char customInputTitle[2][CUSTOM_INPUT_LENGTH];
static unsigned char customInputExtra[2][CUSTOM_INPUT_LENGTH];
const char * payload = "1=Salam Khobi|FC93F8A120F491F3A8=Rial|F191FEA4";
#define CUSTOM_INPUT_REGX       "%d=%[^|]s|%[^=]s=%[^|]s|%s"
static lcdInput customInput = {
        .title = {&customInputTitle[0], &customInputTitle[1]},
        .extra = {&customInputExtra[0], &customInputExtra[1]},
        .type = INPUT_NORMAL,
        .editable = 1,
        .forceLen = 0,
};

int main()
{
    memset(&customInputTitle, 0, CUSTOM_INPUT_LENGTH << 1);
    memset(&customInputExtra, 0, CUSTOM_INPUT_LENGTH << 1);

    sscanf(payload, CUSTOM_INPUT_REGX,
           &customInput.type,
           &customInputTitle[0], &customInputTitle[1],
           &customInputExtra[0], &customInputExtra[1]);

    return 0;
}

Answer 1

"%d=%[^|]|%[^=]=%[^|]|%s"是正确的格式。

Answer 2

问题被问到了

当一个|字符被扫描集指令%[^|]遇到后，sscanf()将恢复与|字符的匹配。下一个指令应该是一个文字|，以避免匹配失败。在原始代码中，使用%[^|]s时，s不是扫描集指令的一部分，相反，sscanf()试图在输入中匹配一个文字s。另外，请注意，应始终在%s和%[] fscanf()系列指令中使用最大宽度说明符，以避免恶意或格式错误输入的缓冲区溢出：

"%d=%39[^|]|%39[^=]=%39[^|]|%39s"

其他一些严重问题

在编译C代码时始终启用警告；这样做可以帮助您避免几个严重的问题。对于这段代码有很多警告，下面列出的大多数问题都会导致未定义的行为。我总是至少使用gcc -std=c11 -Wall -Wextra -Wpedantic，并且在答案的末尾为原始代码添加了gcc输出的示例。

发布的代码缺少#include <string.h> for memset()。

.title和.extra字段的lcdInput应该是unsigned char *，因为它们指向unsigned char数组的第一个元素。

在customInput的初始化过程中，应该删除&操作符。customInput.title和customInput.extra都期望指向unsigned char (或在上述更正之前的chars )的指针。例如，对于&customInputTitle[0]，您有一个指向CUSTOM_INPUT_LENGTH unsigned chars数组的指针(或在上面更正之前的chars )；这是类型不匹配，编译器应该发出响亮的抱怨(启用了警告)。相反，只需使用：

static lcdInput customInput = {
    .title = {customInputTitle[0], customInputTitle[1]},
    .extra = {customInputExtra[0], customInputExtra[1]},
    .type = INPUT_NORMAL,
    .editable = 1,
    .forceLen = 0,
};

在这里，customInputTitle[0]是一个CUSTOM_INPUT_LENGTH unsigned char的数组，它将衰减到指向其第一个元素(unsigned char *)的指针。或者，您可以使用&customInputTitle[0][0]、&customInputTitle[1][0]等。

类似地，您需要在调用customInput时从sscanf()数组中移除这些符号。在这里，您还需要对&customInput.type做些什么。这是一个enum类型，不能输入enum值。同样，编译器会在启用警告时发出抱怨。相反，试着：

int typeInput;
if (sscanf(payload, CUSTOM_INPUT_REGX,
           &typeInput,
           customInputTitle[0], customInputTitle[1],
           customInputExtra[0], customInputExtra[1]) == 5) {
    if (typeInput >= INPUT_NUMBER && typeInput <= INPUT_PAYAMOUNT) {
        customInput.type = typeInput;
    } else {
        /* Handle error */
    }
};

在这里，typeInput用于收集输入，检查sscanf()返回的值以验证是否分配了正确的值，并根据inputType的值范围检查typeInput的值。如果输入与预期的相同，则将typeInput分配给customInput.type。

对memset()的调用将起作用，但是为什么要用位移位来混淆事情呢？这里也不需要&操作符，但在这种情况下，它们是可以的。相反，考虑：

memset(customInputTitle, 0, sizeof customInputTitle);
memset(customInputExtra, 0, sizeof customInputExtra);

这是修正后的代码。这使用gcc -std=c11 -Wall -Wextra -Wpedantic编译时没有警告。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>        // missing header

typedef enum {
    INPUT_NUMBER = 0,
    INPUT_NORMAL = 1,
    INPUT_PASSWORD = 2,
    INPUT_PAYAMOUNT = 3,
} inputType;

typedef struct {
    unsigned char * title[2];    // need unsigned char
    unsigned char * extra[2];
    inputType type;
    unsigned minLen:6;
    unsigned maxLen:6;
    unsigned forceLen:1;
    unsigned editable:1;
    unsigned char data[100];
} lcdInput;

#define CUSTOM_INPUT_LENGTH     40

static unsigned char customInputTitle[2][CUSTOM_INPUT_LENGTH];
static unsigned char customInputExtra[2][CUSTOM_INPUT_LENGTH];
const char * payload = "1=Salam Khobi|FC93F8A120F491F3A8=Rial|F191FEA4";

// bad format string
#define CUSTOM_INPUT_REGX       "%d=%39[^|]|%39[^=]=%39[^|]|%39s"

// & operator not needed
static lcdInput customInput = {
    .title = {customInputTitle[0], customInputTitle[1]},
    .extra = {customInputExtra[0], customInputExtra[1]},
    .type = INPUT_NORMAL,
    .editable = 1,
    .forceLen = 0,
};

int main(void)
{
    // could use improvements
    memset(customInputTitle, 0, sizeof customInputTitle);
    memset(customInputExtra, 0, sizeof customInputExtra);

    // & operators not needed
    int typeInput;
    if (sscanf(payload, CUSTOM_INPUT_REGX,
               &typeInput,
               customInputTitle[0], customInputTitle[1],
               customInputExtra[0], customInputExtra[1]) == 5) {
        if (typeInput >= INPUT_NUMBER && typeInput <= INPUT_PAYAMOUNT) {
            customInput.type = typeInput;
        } else {
            /* Handle error */
        }
    };

    return 0;
}

GCC输出警告

下面是问题中发布的原始程序中带有gcc -std=c11 -Wall -Wextra -Wpedantic的编译器警告：

bad_program.c:27:19: warning: initialization from incompatible pointer type [-Wincompatible-pointer-types]
         .title = {&customInputTitle[0], &customInputTitle[1]},
                   ^
bad_program.c:27:19: note: (near initialization for ‘customInput.title[0]’)
bad_program.c:27:41: warning: initialization from incompatible pointer type [-Wincompatible-pointer-types]
         .title = {&customInputTitle[0], &customInputTitle[1]},
                                         ^
bad_program.c:27:41: note: (near initialization for ‘customInput.title[1]’)
bad_program.c:28:19: warning: initialization from incompatible pointer type [-Wincompatible-pointer-types]
         .extra = {&customInputExtra[0], &customInputExtra[1]},
                   ^
bad_program.c:28:19: note: (near initialization for ‘customInput.extra[0]’)
bad_program.c:28:41: warning: initialization from incompatible pointer type [-Wincompatible-pointer-types]
         .extra = {&customInputExtra[0], &customInputExtra[1]},
                                         ^
bad_program.c:28:41: note: (near initialization for ‘customInput.extra[1]’)
bad_program.c: In function ‘main’:
bad_program.c:36:5: warning: implicit declaration of function ‘memset’ [-Wimplicit-function-declaration]
     memset(&customInputTitle, 0, CUSTOM_INPUT_LENGTH << 1);
     ^~~~~~
bad_program.c:36:5: warning: incompatible implicit declaration of built-in function ‘memset’
bad_program.c:36:5: note: include ‘<string.h>’ or provide a declaration of ‘memset’
bad_program.c:25:33: warning: format ‘%d’ expects argument of type ‘int *’, but argument 3 has type ‘inputType * {aka enum <anonymous> *}’ [-Wformat=]
 #define CUSTOM_INPUT_REGX       "%d=%[^|]s|%[^=]s=%[^|]s|%s"
                                 ^
bad_program.c:39:21: note: in expansion of macro ‘CUSTOM_INPUT_REGX’
     sscanf(payload, CUSTOM_INPUT_REGX,
                     ^~~~~~~~~~~~~~~~~
bad_program.c:25:33: warning: format ‘%[^|’ expects argument of type ‘char *’, but argument 4 has type ‘unsigned char (*)[40]’ [-Wformat=]
 #define CUSTOM_INPUT_REGX       "%d=%[^|]s|%[^=]s=%[^|]s|%s"
                                 ^
bad_program.c:39:21: note: in expansion of macro ‘CUSTOM_INPUT_REGX’
     sscanf(payload, CUSTOM_INPUT_REGX,
                     ^~~~~~~~~~~~~~~~~
bad_program.c:25:33: warning: format ‘%[^=’ expects argument of type ‘char *’, but argument 5 has type ‘unsigned char (*)[40]’ [-Wformat=]
 #define CUSTOM_INPUT_REGX       "%d=%[^|]s|%[^=]s=%[^|]s|%s"
                                 ^
bad_program.c:39:21: note: in expansion of macro ‘CUSTOM_INPUT_REGX’
     sscanf(payload, CUSTOM_INPUT_REGX,
                     ^~~~~~~~~~~~~~~~~
bad_program.c:25:33: warning: format ‘%[^|’ expects argument of type ‘char *’, but argument 6 has type ‘unsigned char (*)[40]’ [-Wformat=]
 #define CUSTOM_INPUT_REGX       "%d=%[^|]s|%[^=]s=%[^|]s|%s"
                                 ^
bad_program.c:39:21: note: in expansion of macro ‘CUSTOM_INPUT_REGX’
     sscanf(payload, CUSTOM_INPUT_REGX,
                     ^~~~~~~~~~~~~~~~~
bad_program.c:25:33: warning: format ‘%s’ expects argument of type ‘char *’, but argument 7 has type ‘unsigned char (*)[40]’ [-Wformat=]
 #define CUSTOM_INPUT_REGX       "%d=%[^|]s|%[^=]s=%[^|]s|%s"
                                 ^
bad_program.c:39:21: note: in expansion of macro ‘CUSTOM_INPUT_REGX’
     sscanf(payload, CUSTOM_INPUT_REGX,
                     ^~~~~~~~~~~~~~~~~