假的strcmp结果时字符串相等 [英] strcmp results in false when strings are equal

问题描述

这是我的code：

 如果（STRCMP（PCH，地图[我]。名称）== 0）{
            的printf（平等\\ n）;
            返回0;
        }
 

PCH 从文件中读取，地图[我]。名称有64的已知大小。
该字符串大小低于63的比较这两个字符串时比64小的伟大工程：

file11111111111111111111111111111111111111111111111111111111111 和

  file11111111111111111111111111111111111111111111111111111111111
 

一切是桃色和如预期的结果是相等的，但是当这两个（尺寸64）进行比较：

file111111111111111111111111111111111111111111111111111111111111 和

  file111111111111111111111111111111111111111111111111111111111111
 

返回的是假的。
我想这样做的：

 如果（STRNCMP（PCH，地图[I] .name和64）== 0）{
            的printf（平等\\ n）;
            返回0;
        }
 

和它的工作，为64确切大小的字符串，但字符串
较小的结果是随机的。
我在这里处理什么样的诡诈的？

编辑：这是充满code：

 的char * PCH;
    焦炭tempFilesNeeded [100 * 64 + 100];
    的strcpy（tempFilesNeeded，地图[I] .filesNeeded）;
    PCH = strtok的（tempFilesNeeded，，）;
    而（PCH！= NULL）
    {
        如果（STRCMP（PCH，地图[我]。名称）== 0）{
            的printf（平等\\ n）;
            返回0;
        }        PCH = strtok的（NULL，，）;
    }
 

解决方案

好吧，如果这是

 字符PCH [64];
 

那么你就不能在那里有64个可见字符，因为需要终止的最后一项。如果你确实有file111111111111111111111111111111111111111111111111111111111111数组中，它没有终止，并要求的strcmp（）它调用未定义行为

此外，作为一个小点，他说，的strcmp（）返回假是错误的，因为它的回报的不的布尔值。它返回两个第一不同字符之间的关系;如果没有字符不同的字符串相等，则返回零。

This is my code:

        if(strcmp(pch,map[i].name)==0){
            printf("Equal\n");
            return 0;
        }

pch is read from a file, map[i].name has a known size of 64. This works great for strings smaller than 64. when comparing these two strings below of size 63:

file11111111111111111111111111111111111111111111111111111111111 and

file11111111111111111111111111111111111111111111111111111111111

everything is peachy and the result as expected is equal, but when these two (of size 64) are compared:

file111111111111111111111111111111111111111111111111111111111111 and

file111111111111111111111111111111111111111111111111111111111111

the return is false. I thought of doing:

        if(strncmp(pch,map[i].name,64)==0){
            printf("Equal\n");
            return 0;
        }

And it does work for strings of exact size of 64, but for strings that are smaller the result is random. What kind of quirkiness am i dealing with here?

EDIT: this is the full code:

    char * pch;
    char tempFilesNeeded[100*64+100];
    strcpy(tempFilesNeeded,map[i].filesNeeded);
    pch = strtok(tempFilesNeeded,",");
    while (pch != NULL)
    {
        if(strcmp(pch,map[i].name)==0){
            printf("Equal\n");
            return 0;
        }

        pch = strtok (NULL, ",");
    }

解决方案

Well, if it's

char pch[64];

then you can't have 64 visible characters in there, since the last entry is needed for the termination. If you do have "file111111111111111111111111111111111111111111111111111111111111" in that array, it's not terminated and calling strcmp() on it invokes undefined behavior.

Also, as a minor point, saying that strcmp() returns "false" is wrong, since its return is not boolean. It returns the relation between the two first differing characters; if no characters differ the strings are equal, then it returns zero.

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