这次栽倒在sscanf函数上------ 看看错误的语句：int nRet = sscanf("xxx=yyy", "%s=%s", szKey, szValue);

最新推荐文章于 2023-07-09 21:55:30 发布

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本文详细探讨了sscanf函数在不同场景下的使用方法及注意事项，通过实例展示了如何正确解析包含键值对的字符串，并进行了错误排查。重点强调了在字符串中使用变量作为分割符的重要性。

之前用sscanf也是得心应手的，比如：

[cpp] view plain copy

print ?

#include <stdio.h>
#include <string.h>
int main()
{
char szLine[100] = {0};
int left = 0;
int right = 0;
strncpy(szLine, "123=456", sizeof(szLine) - 1);
int nRet = sscanf(szLine, "%d=%d", &left, &right);
printf("nRet is %d\n", nRet);
printf("left is %d, right is %d\n", left, right);
return 0;
}

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

int main()
{
	char szLine[100] = {0};
	int left = 0;
	int right = 0;

	strncpy(szLine, "123=456", sizeof(szLine) - 1);
	int nRet = sscanf(szLine, "%d=%d", &left, &right);
	printf("nRet is %d\n", nRet);
	
	printf("left is %d, right is %d\n", left, right);

	return 0;
}

结果很正常：

nRet is 2
left is 123, right is 456

现在，碰到了字符串，所以我随心所欲地类比写成：

[cpp] view plain copy

print ?

#include <stdio.h>
#include <string.h>
int main()
{
char szLine[100] = {0};
char szKey[50] = {0};
char szValue[50] = {0};
strncpy(szLine, "xxx=yyy", sizeof(szLine) - 1);
int nRet = sscanf(szLine, "%s=%s", szKey, szValue);
printf("nRet is %d\n", nRet);
if(0 == strcmp(szKey, "xxx"))
{
printf("yes, key\n");
}
if(0 == strcmp(szValue, "yyy"))
{
printf("yes, value\n");
}
return 0;
}

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

int main()
{
	char szLine[100] = {0};
	char szKey[50] = {0};
	char szValue[50] = {0};

	strncpy(szLine, "xxx=yyy", sizeof(szLine) - 1);
	int nRet = sscanf(szLine, "%s=%s", szKey, szValue);
	printf("nRet is %d\n", nRet);
	
	if(0 == strcmp(szKey, "xxx"))
	{
		printf("yes, key\n");
	}

	if(0 == strcmp(szValue, "yyy"))
	{
		printf("yes, value\n");
	}

	return 0;
}

结果为：

nRet is 1

从结果看，解析失败，为什么呢？原来此时=并没有做分割符，而是做了szKey的一部分，此时szValue仍然是空串。那该怎么改呢？如下：

[cpp] view plain copy

print ?

#include <stdio.h>
#include <string.h>
int main()
{
char szLine[100] = {0};
char szKey[50] = {0};
char szValue[50] = {0};
strncpy(szLine, "xxx=yyy", sizeof(szLine) - 1);
int nRet = sscanf(szLine, "%[^=]=%[^=]", szKey, szValue);
printf("nRet is %d\n", nRet);
if(0 == strcmp(szKey, "xxx"))
{
printf("yes, key\n");
}
if(0 == strcmp(szValue, "yyy"))
{
printf("yes, value\n");
}
return 0;
}

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

int main()
{
	char szLine[100] = {0};
	char szKey[50] = {0};
	char szValue[50] = {0};

	strncpy(szLine, "xxx=yyy", sizeof(szLine) - 1);
	int nRet = sscanf(szLine, "%[^=]=%[^=]", szKey, szValue);
	printf("nRet is %d\n", nRet);
	
	if(0 == strcmp(szKey, "xxx"))
	{
		printf("yes, key\n");
	}

	if(0 == strcmp(szValue, "yyy"))
	{
		printf("yes, value\n");
	}

	return 0;
}

结果为：

nRet is 2
yes, key
yes, value

以后还是要小心啊，定位较长时间，才发现是栽倒在这个最简单的地方。