【发布时间】：2015-04-26 01:30:51
【问题描述】：
我知道strlen 计算直到（并且不包括）空字符'\0'（或0）的字符数，并且sizeof 给出了存储字符串所需的空间量，包括空字符字符，但我对我的代码的输出感到困惑。
问题：
我希望 strlen 的结果始终比 sizeof 的结果小 1，因为我的字符串以空值结尾，但似乎只有长度为 4 和 8 的字符串是这种情况，不包括 ' \0'（即下面的第 3 和第 5 个结果）。我怀疑这与在第一个、第二个和第三个结果的字符串末尾打印垃圾的原因相同。有人可以解释这种行为吗？
我阅读了这个相关问题，但我不认为这就是这里发生的事情：strlen - the length of the string is sometimes increased by 1。
代码的作用：
在main 中，它创建一个整数数组 0、2、4、6 和 8。然后对于每个长度，它调用函数 make_and_print_msgs 来：
- 创建一个长度为 + 1 的字符串（用于空字符），例如如果长度为 4，则创建字符串“aaaa\0”
- 在
printf中使用%c逐字母打印消息 - 在
printf中使用%s将其打印为字符串 - 找到字符串的
strlen - 找到
sizeof字符串
输出：
i data_length[i]
--------------------
0 0
msg intended to be:
msg printed as string: �
strlen(msg): 1
sizeof(msg): 1
1 2
msg intended to be: aa
msg printed as string: aaS
strlen(msg): 3
sizeof(msg): 3
2 4
msg intended to be: aaaa
msg printed as string: aaaa
strlen(msg): 4
sizeof(msg): 5
3 6
msg intended to be: aaaaaa
msg printed as string: aaaaaai
strlen(msg): 7
sizeof(msg): 7
4 8
msg intended to be: aaaaaaaa
msg printed as string: aaaaaaaa
strlen(msg): 8
sizeof(msg): 9
代码：
（抱歉代码有点长，所以我在上面解释了。代码中的一些 cmets 是对 Python NumPy 函数的引用。）
#include <stdio.h>
#include <math.h> /* needed for ceil */
#include <string.h> /* needed for strlen */
void make_linspace(int a[], double start, double stop, int num) {
/* Fills array a[] (in place) with linearly spaced values just like np.linspace in NumPy (Python) */
double spacing = (stop-start)/(num-1);
int i;
for (i=0; i<num; i++){
a[i] = start + i*spacing;
}
}
void make_and_print_msgs(int n_proc, int msglength)
{
/* Create a string called msg of length msglength + 1 (for the null character '\0') */
char msg[msglength+1];
int i;
printf("msg intended to be: ");
for (i=0; i<msglength; i++) {
msg[i] = 'a';
printf("%c", msg[i]);
}
msg[i+1] = '\0';
/* Print message to screen as a string and fine strlen(msg) and sizeof(msg) */
printf("\n");
printf("msg printed as string: %s\n", msg);
printf("strlen(msg): %d\n", strlen(msg));
printf("sizeof(msg): %d\n\n", sizeof(msg));
}
void main(int argc, char *argv[])
{
int n_proc = 2;
/* Create an array containing the lengths of strings to be printed (In this case, data_length should be {0, 2, 4, 6, 8} */
int start = 0;
int stop_range = 10; /* the stop value if we are using range() */
int step = 2; /* spacing between the integers in the output of range() */
int stop = stop_range - step; /* the stop value if we are using linspace() */
int npoints = (int) ceil( ((double)stop_range - (double)start) / (double)step ); /* number of elements in the list produced by range(start, stop_range, step) */
int data_length[npoints]; /* 1D array of string lengths (# of non-null chars in each str) */
make_linspace(data_length, start, stop, npoints);
int i;
/* For each length, call on make_and_print_msgs to make a string of that length (plus '\0') and then print to stdout */
printf(" i data_length[i]\n--------------------\n");
for (i=0; i<npoints; i++) {
printf("%4d %7d\n", i, data_length[i]);
make_and_print_msgs(n_proc, data_length[i]);
}
}
【问题讨论】：
-
msg[i+1] = '\0';应该是msg[i] = '\0';，因为msglength是msg的最后一个有效索引，i在循环后等于它。 -
天哪！那真是个愚蠢的错误。非常感谢。
-
不要使用
%d打印size_t类型的值。使用%zu。
标签： c string null sizeof strlen