argv | 易学教程

argv pointer to an array of pointers

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问题 I am confused as to how the following passage matches up with the code that follows it: Since argv is a pointer to an array of pointers , we can manipulate the pointer rather than index the array. This next variant is based on incrementing argv, which is a pointer to pointer to char, while argc is counted down: #include <stdio.h> /* echo command-line arguments; 2nd version */ main(int argc, char *argv[]) { while (--argc > 0) printf("%s%s", *++argv, (argc > 1) ? " " : ""); printf("\n"); return

Are the strings in argv modifiable?

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问题 I just wrote a small program that reads command line arguments in C, nothing too difficult. I was also modifying them, for example changing the first character of the parameter to uppercase. I know that you shouldn't modify string literals as it can cause undefined behavior, so was just wondering if the strings in the *argv[] are literals that you shouldn't change. int main(int argc, char *argv[]) 回答1: From the C11 standard draft N1570, §5.1.2.2.1/2: The parameters argc and argv and the

Is Python 'sys.argv' limited in the maximum number of arguments?

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问题 I have a Python script that needs to process a large number of files. To get around Linux's relatively small limit on the number of arguments that can be passed to a command, I am using find -print0 with xargs -0 . I know another option would be to use Python's glob module, but that won't help when I have a more advanced find command, looking for modification times, etc. When running my script on a large number of files, Python only accepts a subset of the arguments, a limitation I first

QApplication app(argc, argv)

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I noticed that the main.cpp in a Qt application has to contain the following line: QApplication app(argc, argv); I know that argc is the number of command-line arguments, and argv is that array list of command-line arguments. But, the question in my mind is: what are those arguments I'm passing to the constructor and at the same time cannot explicitly see? What is working behind the scences out there? Thanks. There are no hidden arguments. You can explicitly see every argument- argc, argv . There's nothing in that line of code that's behind the scenes. From looking at your comments to other

Can argv[0] contain an empty string?

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问题 In any C program, the command line argument argv[0] points to the name used to invoke the program. Is there any circumstance in which it will point to an empty string "" ? An example code snippet for such a case would be a good reference. 回答1: It's implementation defined. §5.1.2.2.1 abridged: If the value of argc is greater than zero, the array members argv[0] through argv[argc-1] inclusive shall contain pointers to strings, which are given implementation-defined values by the host

Memory allocation and **argv argument [closed]

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问题 Closed . This question needs details or clarity. It is not currently accepting answers. Want to improve this question? Add details and clarify the problem by editing this post. Closed 5 years ago . I know for what we use this argument, and I even know how to work with the argument. There is only one things I still do not understand. How a program allocate memory for strings which came from the input. **argv has no allocated memory at the start of the program, isn't it? I was expecting

script full name and path $0 not visible when called

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I have a script "task.sh" with the following content: #!/bin/bash CUR_DIR=`pwd` SCRIPTPATH="${CUR_DIR}/`dirname $0`" when I call it with "bash task.sh" it works as expected but when it is called with ". task.sh" $ . log/task.sh dirname: invalid option -- b Try `dirname --help' for more information. When the script is being scheduled in crontab it is not working as well. Can someone tell me what am I doing wrong or a different way in order to get the directory of a script that is not the current directory ? When you invoke it as bash task.sh , bash assigns "task.sh" to $0 (from the bash manual

Why check if (*argv == NULL)? [duplicate]

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This question already has answers here : When can argv[0] have null? (4 answers) Closed 2 years ago . In the data structures class that I am currently taking, we have been tasked with writing a web crawler in C++. To give us a head start, the professor provided us with a program to get the source from a given URL and a simple HTML parser to strip the tags out. The main function for this program accepts arguments and so uses argc/argv. The code used to check for the arguments is as follows: // Process the arguments if (!strcmp(option, "-h")) { // do stuff... } else if (!strcmp(option, "")) { //

Using argc and argv in Eclipse?

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问题 I have a working program but now I have to use the int argc and char *argv[] parameters to main . Whenever I try to do this it gives me errors that it cannot save. Is there any way to make argc and argv work in Eclipse? 回答1: I guess your problem is that you don't know hot to pass argument to you program, when you execute it through eclipse isn't it ? If that is what you want, read the following. Click on the "Project->Properties" then in "Run/Debug settings" click on the "New button". Choose

Are the strings in argv modifiable?

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I just wrote a small program that reads command line arguments in C, nothing too difficult. I was also modifying them, for example changing the first character of the parameter to uppercase. I know that you shouldn't modify string literals as it can cause undefined behavior, so was just wondering if the strings in the *argv[] are literals that you shouldn't change. int main(int argc, char *argv[]) From the C11 standard draft N1570, §5.1.2.2.1/2: The parameters argc and argv and the strings pointed to by the argv array shall be modiﬁable by the program, and retain their last-stored values